Tài liệu Bulding skill for the toefl ibt transcripts part 2 pdf

Transcripts
647
blood flowing into your stomach slows down. Your muscles
tighten up, ready for action. This is why, after consuming a big
cup of coffee, you feel excited. You can feel your heartbeat
increasing. You’re ready to do something, go somewhere, run,
play, fight, conquer the world....or else start STUDYING to get
ready for the next test!
Skill C
01 Science
W: We use microscopes to help us study cells. Because cells are so
small, we can’t see them without magnification --- um, the ability
to make them look bigger. The first microscopes were called
light microscopes. They were pretty simple devices. They were
also simple to use. Scientists first cut the cells, or specimens,
into thin sections. Then they stained the specimens with different
colored materials, called dyes. The dyes helped them see the
specimens more clearly. Unfortunately, dyes often killed the
cells, too. That limited what scientists could find out about the
specimen. In recent years, we have developed more powerful
microscopes. These help us view living specimens.
One of these new microscopes is called the phase-contrast
microscope. It’s made in such a way that part of the light passing
through it moves more slowly than the rest of the light. We say
this part of the light is “out of phase” with the rest of the light.
This enables scientists to see differences in living specimens as
light and shade. Another type of new microscope is the electron
microscope. This uses electrons to form images, instead of
light. Electrons travel in waves, similar to light, but their
wavelengths are over 100,000 times shorter than those of
light. Therefore, they can give much clearer magnification.

Electron microscopes even allow scientists to take pictures of
the cells they are studying!
02 Campus Life
W: Hey Frank. If you could be any person in the world, who would
you be?
M: That’s easy. Bill Gates!
W: Why?
M: I’ll give you 30 billion reasons. Ha, ha.
W: Ah, so it’s the money.
M: Not totally. But the money is nice. I was reading that if you made
all of Gates’ money one-dollar bills, and then laid them end-to-
end, the line would stretch for almost six million kilometers.
W: Wow! But what would you do with all that money?
M: Gates gives a lot to the poor. He’s donated almost seven-and-
a-half billion since the year 2000. I’d give away even more.
W: Really?
M: Sure! It costs about $240 a year to feed a starving child. So, Bill
could save almost 121 million children.
W: Hmm...why else do you like Gates?
M: I admire his confidence. Did you know he earned a scholarship
to Harvard, but left after two years to start Microsoft? That
took courage!
03History
M: So, you’ve heard of the Gettysburg Address. But do you know
the story behind it?
The worst battle of the American Civil War was fought in
Gettysburg, Pennsylvania. The Northern Army fought back the
Southern Army. The battle lasted three days. Afterward, the
field was left covered with bodies of dead soldiers.
In November 1863, President Abraham Lincoln came to Gettysburg.

He was to speak at the opening of the cemetery there. Music
played and soldiers saluted. Edward Everett, governor of
Massachusetts, talked first for almost two hours.
Then Lincoln stood up. He looked out over the valley. Then, he
began to speak. He said they couldn’t do anything to make this
place special. He said that the soldiers who had fought so hard
had already done that.
He said that everyone would soon forget what was spoken
that day, but he said that what the soldiers did would never be
forgotten. He said everyone should keep doing what these
soldiers began. They should keep fighting for freedom for all
the people. Then, they could make sure the soldiers didn’t die
needlessly.
The president’s speech only lasted two minutes! Everyone
cheered and then left. Lincoln turned to Edward Everett. He
said he thought he should have planned his speech better.
Edward Everett didn’t agree. He said, “It was perfect. You said
more in two minutes than I did in two hours.”
Afterward, the newspapers said it was a great speech. And, as
you know, Americans still remember it today.
04 Phys. Ed.
W: Some people are surprised to know that walking is very good
exercise. It seems very easy, but it does us a lot of good. It
cleans the blood, tones up muscles, and strengthens bones. It
even helps people lose weight. One study showed that fast
walking keeps your heart healthy. Men who walked fast were
50 percent less likely to have heart disease.
You don’t need much equipment to do it, and almost anyone,
anywhere, at any time, can do it.
It’s not difficult to plan walks into your day. You can walk to

work, to catch a train, or to a park. You can walk to shops or
enjoy walks in the country. It’s a great way to spend time with
family and friends. People have some of their best conversations
while walking.
It’s best to do some stretches before and after you walk. Take
short quick steps, stand straight, and take deep breaths.
For basic health, it’s good to walk most days of the week. Walk
for 20 to 30 minutes or more at a “talking pace.”
To lose weight, walk for 30 to 45 minutes or more. Walk as
many days as you can. Walk fast enough so that you finish
slightly out of breath.
To make your heart stronger, walk quickly for 20 minutes or
more. If you can, walk where there are some small hills. Walk
two or three times a week. Go as fast as you can, but enjoy
yourself. Exercise should never be painful.
05 Campus Life
W: Josh, what are you doing tonight?
M: I have a biology class. What are you doing?
W: Well, my friend’s sorority is having a party, but I don’t want to
walk by myself in the dark.
M: Why don’t you use Campus Escort?
W: What’s that?
M: Campus Escort is a free service that gives students rides. Other
students drive you to the place you’re going.
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W: Really? It’s free?
M: Yep. Just call 874-SAFE and tell them what time you would like
to be picked up.
W: But...will they escort me back home?

M: Sure. There’s a car that will take you from your dorm room to
the party, then back to your dorm. It runs 5 p.m. to 1 a.m. And
there’s a small van that picks students up each hour at the student
center and the mall. It runs from 6 p.m. to midnight.
W: What if I want to stay later?
M: Call campus police for a free escort: 874-2121.
06 General Studies
M: All right. Saturday’s the big day. Are you ready? Yes, Susan?
W: Tests make me nervous. What can I do?
M: Good question. It’s natural to be a little nervous before a test.
The important thing is: don’t panic. You’ve studied hard for this
test. You can pass it. Be confident! Relax! Now, you’re more
likely to be relaxed if you are well prepared. Here are some tips.
First, before you leave home, check to make sure you have
everything you need. You should have your admission ticket.
This was mailed to you last week. You should have two
number-two pencils and a good eraser. You should have
identification --- your student ID card, a driver’s license, or a
passport. If you’re taking the math portion of the test, you
should have a calculator.
Second, know what you can’t bring to the test. You cannot
bring a watch with a loud alarm. You cannot bring any food or
drink. You cannot bring extra paper to write on. You cannot bring
any books, notes, or dictionaries. You cannot bring compasses,
rulers, protractors, or other aids --- except for the calculator.
You cannot bring colored pens, pencils, or highlighters. You
cannot bring cell phones or pagers. You cannot bring any portable
tape recorders, walkmans, or headphones. Questions?
W: Um...what if I uh, have to go to the bathroom during the test?
M: You can’t. So go before! Don’t worry, there will be breaks after

each section of the test. You’ll be able to go then.
Chapter 2
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01 Campus Life
M: All right. Here’s your student ID card. You’ll need to show this at
every meal, or each time you buy something at a campus dining
hall.
W: Really? Hmm. That’s different than my old school.
M: Yes, I imagine it is. We have a unique system here. Do you
know about our meal plans?
W: Meal plans? Uh, no.
M: There are several different plans. You can choose to buy 9, 12,
15, or 18 meals each week. It depends on your schedule and
eating habits.
W: I see. Um, what if I buy the 15-meal plan and only eat 13 meals
that week? Will I get 17 the next week?
M: No, meals do not carry over into the next week. That’s why it’s
important that you choose your meal plan carefully.
W: What if I want to treat my friend? Can I use two meals at one time?
M: Sorry, no. Only one meal each meal period. If you want to treat
a friend, you can use your declining balance points.
W: My what?
M: Declining balance points. They work like an ATM card. At the
dining halls, you use the points like cash. You can buy food,
snacks, or meals. Then the points are withdrawn from your
declining balance account. All of our meal plans offer these

points.
W: Um, OK. What happens when I run out of declining balance
points?
M: You can buy more points at any time. Just go to the One Card
office on the North Campus. We will bill your home through
the Student Accounts office.
02 Geography
W: We usually think of deserts as hot, dry, sandy places. And many
deserts are. But actually, deserts come in several forms. Let’s learn
about some of them.
In defining a desert, we have to consider two factors. The first
is the annual amount of rainfall. Deserts get less than 250
millimeters of rain or snow each year. The second factor is how
much of that rain or snow evaporates --- that is, goes back into
the atmosphere or is used up by plants. We call this loss of
water “evaporation.”
Simply stated, a desert is a place where evaporation is greater
than rainfall or snowfall. Because so much water evaporates,
most deserts are hot. But not all. The North and South poles,
for instance, are cold deserts. They get less than 250 millimeters
of snow each year, and the ground is permanently frozen.
We also classify deserts by their location and main weather pattern.
One example is trade wind deserts. Trade wind deserts are
located between 30 degrees and 35 degrees north and south
of the equator. The winds that blow over these areas are very
strong. They blow away clouds, so more sun reaches the ground.
Most of the major deserts in the world lie in the areas crossed by
the trade winds. The Sahara Desert, in North Africa, is a trade wind
desert. Temperatures there can reach 57 degrees Celsius.
Another type of desert is the rain shadow desert. Rain shadow

deserts lie next to tall mountains. As clouds rise over the mountains,
they spill all of their rain or snow before they get to the other
side. So, these deserts are formed in the “shadow” of the
mountains. The Judean Desert in Israel is a rain shadow desert.
So is a large part of the western United States called the Great
Basin.
Still another kind of desert is the coastal desert. Coastal deserts
are on the western edges, or coasts, of continents. One coastal
desert, the Atacama Desert of South America, is Earth’s driest
desert. In the Atacama, there can be measurable rainfall only
once every 50 years.
03Business Writing
M: Today, I’d like to give you some basic rules for writing a resumé.
Let’s begin with spelling. Don’t use words you don’t know. Use
a dictionary. Seems like a lot of trouble to get up, find a dictionary,
and look up the word. But if you’re on the computer, you can
look up words online. Do a spell check, but then read every
word carefully. The spell check can’t catch every mistake. If you
use “form” instead of “from,” it won’t catch it. So, use a spell
check, but read everything yourself, too. And read carefully. If you
read quickly, it’s easy to miss words that are misspelled. Have a
friend read your resumé, too.
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Another thing, choose your words carefully. Some words sound
alike but don’t mean the same thing, like these: personal means
private, personnel means staff members. And use active tense
like “directed staff” rather than passive tense like “was staff
director.” The active tense gives a stronger feeling.
Now, about grammar. In each part of your resumé, keep the

same tense. The duties you do now should be in the present
tense. Things you did in the past should be in the past tense. For
example, let’s say you started your job several years ago in
September. You might write on your resumé “September 2003
to present, manage office and staff,” or “teach at Canyon High
School.” That means, “I manage” or “I teach” now. But if
you’re listing a job you don’t have anymore “taught at Canyon
High School” instead of “teach at Canyon High School.”
Don’t give your sex, age, race, or marital status. How much
money you made before is also personal information.
Make your resumé look nice. Make it as simple as you can, too.
Leave plenty of space, but try to make it just one page. Use a
font like Times Roman that’s easy to read. Put your name,
address, and telephone number on it and any letters. Use a
good printer and print on only one side of white paper. Your
resumé speaks for you. A professional-looking resumé tells an
employer that you do things well. An employer may decide to
see you or not because of it.
0
4 Economics
W: Our world is so rich! All the people together make more than
$31 trillion a year. In some countries, many people make more
than $40,000 a year. But in other countries, many people make
less than $700 a year. Of these, 1.2 billion earn less than $1.00
a day. Because of this, 33,000 children die every day in these
poorer countries. Each minute, more than one woman dies in
childbirth. Being poor keeps more than 100 million children out
of school. Most of them are girls.
Helping the poorer countries is a very big task --- especially
because more people are born every year. In fifty years, there

will be about 3 billion more people.
The World Bank is a bridge between the rich and poor people.
It’s making rich-country money into poor-country growth. It is
one of the world’s biggest banks for poor countries. It’s helping
them build schools and health centers, and get water and
electricity. It’s helping protect the people’s surroundings.
The low-income countries can’t usually borrow money in world
markets. If they do, they have to pay very high interest rates.
The World Bank gives them some money, low-interest loans,
and interest-free credit. It helps them take care of the money,
too. When the countries get loans, they have 35---40 years to
pay them back. They can have ten extra years if they need it.
In the year 2002, the bank agreed to give about $15 billion to
low-income countries. For some of the poorest countries, AIDS
is a very big problem. Some of this World Bank money is to
help them fight this disease. If they don’t receive help, many
more people will get the illness.
The World Bank is not like other banks. It’s really a part of the
United Nations. One hundred and eighty-four countries belong
to it. These countries all put money into it and help maintain it.
About 10,000 people work in World Bank offices. They are
from nearly every country in the world. Its headquarters is in
Washington, DC. But there are World Bank offices in 109
countries.
Skill D
01 Campus Life
W: Hi Tony! Where are you headed?
M: Hey, Mary. I’m going to the campus gym to lift weights. Want to
come? Um, there’s an aerobics class at 5 o’clock.
W: Uh, no thanks. I’ve got to study for my chemistry mid-term.

Maybe next time. How often do you go?
M: I try to go three times a week. When I study, I sit too much. I
don’t feel good unless my body gets some exercise, not just my
mind.
W: Do you usually just lift weights?
M: No. I lift to get stronger. Then, I run on the treadmill to help my
heart and lungs. Then, I jump rope or do aerobics to improve
my balance and coordination.
W: Wow! I wish I had that much discipline.
M: Start slowly and do a little more each day.
W: Thanks for the advice. Well, have fun. Maybe I’ll go next week.
M: Bye! Good luck on your mid-term.
02 Physical Science
W: Rocks wear down and break apart due to a process called
weathering. There are two main types of weathering: mechanical
and chemical.
Mechanical weathering involves the disintegration, or destruction,
of rocks by mechanical processes. These include the freezing
and thawing of water in the crevices --- uh, holes and cracks ---
of rocks. Also, the roots of plants can cause rocks to break
apart. The tiny, hair-like roots grow into small cracks in rocks.
Then, as the roots get bigger, the roots crack the rocks. Animals
are also responsible for mechanical weathering. They burrow, or
dig, into the rocks and the dirt around the rocks. Mechanical
weathering is especially common in high altitudes, where it’s so
cold that freezing and thawing happen every day. It’s also common
in deserts, where there is little water and few plants.
Chemical weathering involves the decomposition of rock by
chemical changes or solution. This includes the processes of
oxidation, carbonation, and hydration. For example, many iron

minerals found in rocks are rapidly oxidized, meaning they can
quickly turn to rust. It sounds funny, but rocks can rust or oxidize.
Then, there is carbonation. Limestone is a rock that does this.
Limestone is a type of rock that is dissolved by water, which
contains carbonic acid. We’ll go into more detail about that
reaction later. Anyway, chemical weathering takes place in
warm, wet conditions. In general, chemical weathering is more
common than mechanical weathering, although they usually
act together.
03 Campus Life
M: I just don’t get it!
W: Get what?
M: Professor Johnson’s biology lecture. I took notes, but I don’t
understand them.
W: You should go to a review session.
M: A review session?
W: Yeah. A review session is a discussion that’s led by a student
who has already taken the class. They review the professor’s
lecture and the homework assignments for each week. Then,
they answer questions.
M: It sounds like an extra class.
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W: You don’t have to go, but if you’re having trouble, a review
session will help you a lot. I went to one last year when I had
Professor Johnson’s class.
M: Yeah? How did you do?
W: I got an A-minus.
M: Hmm. When is the review session?
W: Let’s see... You have your choice. You can go Monday from 5

to 6 p.m., or Tuesday from 3 to 4.
M: I’ve got economics on Tuesday. I guess I could go Monday.
W: It’s up to you.
M: I’ll think about it.
04 Business
M: Advertisements. They’re everywhere. You can’t hide from them.
There’s no escape. Turn on the TV. There they are. Turn on the radio.
There they are. Waiting for an elevator? There they are. Using your
computer? There they are. Looking out your car window?
Ahhhhhh! Ads, ads, ads! Aren’t you getting tired of them?
W: Yes! Especially on my computer and on TV. I wish there weren’t
so many of them.
M: Well, would you believe you’ve actually seen more ads than you
think? You’ve also been watching secret ads. Instead of regular
ads, today we are seeing lots more of something called product
placement. Product placement is like an ad that’s not an ad. It’s
an advertisement in disguise. For example, how many of you
have seen the movie Cast Away, with Tom Hanks? Mmmm,
most of you. Which company does Toms Hanks work for at the
start of the movie?
W: Fed Ex.
M: Bingo! That’s a product placement. Fed Ex --- short for Federal
Express --- got more publicity from that movie than it could have
with hundreds of traditional ads. In another movie, The Firm, the
main character drank a beer from Jamaica called Red Stripe. In the
movie’s first week, sales of Red Stripe increased 50 percent. Product
placement used to be limited to movies. Now, we see it on TV
shows, video games, even in books. It’s an effective technique.
But companies have to be careful. They want their products to
be visible within a scene, but not the focus of attention. When

done correctly, product placement can add a sense of realism
to a movie or television show that something like a bottle simply
marked “beer” cannot.
05 Music
M: Today we’re going to learn about a kind of song called a ballad. A
ballad is a song that tells a story. Usually, the story in a ballad is one
that began with oral tradition. Parents passed it down to their
children from generation to generation. Ballads are often sung in
rhyme, like a poem. Unlike a poem, though, ballads do not use a
lot of explanation. The words are usually simple, clear, and easy
to read. There is not much emotion. And the motives of characters
--- that is, why they do something --- is not usually told. One
famous ballad from the 1800s is called “Shenandoah.” Um,
S-H-E-N-A-N-D-O-A-H. It tells the story of a white man who was
in love with an American Indian woman. She lived near the
Missouri River, one of the two largest rivers in the United States.
Listen to part of the song:
The white man loved an Indian maiden
Away, you rolling river
With notions his canoe was laden
Away, I’m bound away
Cross the wide Missouri
O Shenandoah, I love your daughter
Away, you rolling river
For her I’ve crossed the rolling water
Away, I’m bound away
Cross the wide Missouri
Notice the dialog in the second verse. The white man tells his
lover’s father: “Oh Shenandoah, I love your daughter...for her I’ve
crossed the rolling river.” Such dialog is typical of ballads. So, we

have three characteristics of ballads so far. One, they tell a story.
Two, they come from oral tradition. Three, they repeat simple
words and use dialog.
06 Earth Science
M: Trade winds are a pattern of wind found in regions near the
Earth’s equator. Do you remember what the equator is?
W: The imaginary circle around the middle of the Earth that divides
the planet into the northern hemisphere and southern
hemisphere.
M: Very good! Now, in the old days, sailors used to sail their boats
back and forth across the equator on their way to trade things
with other nations. They depended on the wind to get them
there quickly. Hence the name, trade winds. The trade winds
begin in regions called the Horse Latitudes. These are regions
between 30 degrees and 35 degrees north and south of the
equator. The winds in the Horse Latitudes are light, and the
weather there is hot and dry. Because of the light winds, trading
ships would become stalled in the Horse Latitudes. Sailors were
worried about running out of water, so they threw their horses
into the sea. This way, they could drink the water meant for the
horses. It also made their boats lighter, so they could go faster.
The trade winds blow from the Horse Latitudes toward the
equator. In the Northern Hemisphere, they blow from the
northeast and are called the Northeast Trade Winds. In the
Southern Hemisphere, they blow from the southeast and are
called the Southeast Trade Winds. The trade winds between
about 30 degrees latitude and the equator are steady and blow
about 22 to 24 kilometers per hour. They can quickly propel
ships across the ocean.
Skill E

01 Campus Life
M: Excuse me. I’d like to buy a bicycle permit please.
W: That will be four dollars.
M: Here you are. And the permit will let me park my bike anywhere
on campus?
W: Yes.
M: How long is the permit valid for?
W: It’s valid for the next four years. OK, now I need your bicycle
serial number.
M: My serial number? Just a minute. Ah, here it is. A7-10023.
W: All right. Next, I need some identification with your address on it.
M: My address? Um, oh yeah. I have my driver’s license.
W: Sure, your driver’s license will be fine...all right. Last but not
least, you need to fill out this bicycle registration card. Then
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we’ll give you your permit.
M: Here you are.
W: Thank you. Now, you need to make sure this permit is in plain
sight on your bicycle. Attach it to the main frame, on the center
post below the seat. If we can’t see it, you will have to pay a fine.
M: No problem. Thanks.
02 Art
W1: Today, we’re going to see how much you know about china.
M1: It’s got the Great Wall.
W2: And rice.
M2: And chopsticks!
W1: No, not that China. Yes, China is a country. But there’s another
china-the kind you eat off of. This china is a fancy type of
porcelain. Porcelain is a material used to make plates, cups, and

bowls. When people get married in America, one of the oldest
customs is for the bride and groom to choose which type of
china they want for their new home.
There are four main processes in creating china. These are clay
making, mold making, glazing, and decorating. In the clay-making
process, five ingredients are mixed together with water and
shaped into tubes. These tubes are called pugs: P-U-G-S. In the
mold-making process, plaster is poured into metal molds to
make production molds. These production molds are then used
to shape the pugs into plates, cups, and bowls. Next, comes the
glazing process. Glaze is like liquid glass. When it’s heated,
glaze forms a protective shell around each piece of china. Glaze
is incredibly strong. A store in Canada once showed how strong
china is by using four teacups to support a race car! Can you
picture that---a heavy car with only one small cup under each
wheel? After glazing, the china is ready for decorating. Here,
artists use 85 patterns and 400 different shapes to make the
china look beautiful. Then, it’s ready to be sold.
03 Campus Life
M: I’d like to check out this book, please.
W: May I please see your student ID card?
M: I’m sorry, ma’am, it’s been stolen. It was in my wallet, which
was stolen.
W: I’m not allowed to check out any books for you without it.
M: Oh, that’s great! What should I do now?
W: You can download the form for a new student ID card from the
computer. Fill it out and take it over to the Student Center.
Actually, they can also give you the form there.
M: Thanks. I don’t think I’ll bother. Doesn’t it cost $10.00?
W: It does. You might just want to do it, though. You won’t be

allowed to sit for exams without it.
M: All right, I guess I’ll have to. I suppose they’ll want a passport
photo too.
W: Yes, and a copy of your identification --- driver’s license or passport.
M: All right, I’ll go over there. Thanks ma’am.
W: You’ll be glad to have it. Good luck!
04 Health
M: Let’s begin our study of Vitamin D. It’s something we must have.
Among other things, it helps our bodies use the important min-
eral, calcium. Calcium makes our bones strong. It also helps our
nerves and muscles work the way they should.
Let’s open our textbooks to page 63. I’d like you to take a look
at these pictures. As you can see, these children don’t look well
at all. The bones in their heads haven’t come together as they
should. That’s why their heads are too big. Their legs curve out.
The bones are too soft to stand on. These children didn’t get
enough Vitamin D. Happily, we don’t see this too often any more.
Vitamin D is not in most of the foods we eat. We get it mostly
from the sun. Ultraviolet rays from the sun transform something
in our skin. It becomes what’s called previtamin D3. Inside our
bodies, it changes again. It becomes what’s called active vitamin
D. With active vitamin D, our bones can make enough calcium
to stay hard. Active vitamin D helps us have enough calcium for
our nerves too. This helps us feel calm and sleep well.
Today, many people need to have stronger bones. Many older
people’s bones, especially, break far too easily. One main reason
why is that people don’t get nearly enough sunlight. We close
windows to stay warm in the winter. In summer, we close
windows for air conditioning. But we really need time in the
sunshine almost every day.

05 Computer Science
W: I did a search on Google yesterday. It was amazing. I typed in
“horses” and hit the search button. In less than a second, it
showed me more than 32 million websites related to horses. Do
you ever wonder how computers can think so fast? Well, I did
another Google search, and I found out.
Computer chips are based on something called Boolean logic.
This is a type of thinking developed in the mid-1800s by
George Boole --- B-O-O-L-E. Boolean logic maps information
into bits and bytes.
It begins with seven electronic pathways, called gates. The
simplest gate is called a NOT gate. The NOT gate takes one bit
of input, which we’ll label A, and produces an output, which
we’ll label Q, that is exactly opposite. So, if input, A, is one, the
output, Q, will be zero. If A is zero, Q will be one. Simple. Next
is the AND gate. The idea behind an AND gate is this: if there
are two bits of input, say, A and B, and if A and B are both the
same, then the output, called Q, should be the same. After the
NOT gate and the AND gate comes the OR gate. Its basic idea
is, “If A or B is one, or if both A and B are one, then Q is also
one.” The next two gates are called NAND and NOR. These two
gates are simply combinations of an AND or an OR gate with a
NOT gate. Now, next comes....
06 Biology
M: Let’s begin. Last week, we learned how most fish use their swim
bladder to move around in the water. Remember, when the fish
breathes oxygen, some of that oxygen goes into its bladder. This
causes the fish to rise in the water. When it squeezes some of
the gas out of its bladder, it sinks toward the bottom. So, it can
move vertically --- go up and down --- kind of like a hot-air

balloon.
A shark is more like an airplane. Sharks don’t have a swim bladder,
so they use their forward movement to control their vertical
position. The tail is like the shark’s propeller. The shark swings it
back and forth to move forward. In an airplane, this forward
movement pushes air around the wings. For a shark, this forward
movement pushes water around the fins. In both cases, the
forward movement creates lift --- the airplane and shark both rise.
Sharks have two pairs of fins on each side of their bodies. These
fins are in about the same position as the main wings and tail
wings on an airplane. The shark can position these fins at different
angles. This changes the path of the water around them and