unit18
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unit18-1.----------
Title：1.Tang Ming and Du Hua, two college students, are discussing computer craze.
Question：What negative effect does computer bring to the college students?
Question：What do the colleges do to deal with this problem?
Question：What do Du Hua and Tang Ming think about the reason?
Woman：Tang Ming
Man：Du Hua
Tang Ming：
Now, many students have computers.
A computer craze has hit the campus of many colleges in China.
Du Hua：
Yes, you are right.
If you enter a dormitory, you will find one or two computers there.
Tang Ming：
It is true that the computer has been used widely in students' studies.
But some students often play computer games.
Du Hua：
Right.
According to the survey, computers greatly influence some students' studies.
In my university, many young video addicts could indulge themselves in games all night long.
Tang Ming：
Oh.
Fortunately, many universities and colleges are aware of such problems and are planning to carry out projects to correct this phenomenon.
Du Hua：
It seems to me that the campus computer problems are not a question of the computer itself but of the way of using it.
Tang Ming：
I agree.
We are sure that colleges and universities can find a good solution to these problems.
unit18-2.----------
Title：2.Wu Li is a salesman. Ma Gang is a customer. They are talking about exchanging a computer.
Question：What does Ma Gang complain about?
Question：Did Ma Gang try the computer in the store?
Question：Does Wu Li agree to change the computer for another one?
Woman：Wu Li
Man：Ma Gang
Wu Li：
What can I do for you?
Ma Gang：
I bought a computer here last Friday and now it simply does not work.
Wu Li：
What's wrong with it?
Ma Gang：
I'm not sure.
When I turn it on, there's only sound but no words.
Wu Li：
Is the screen clear?
Ma Gang：
Not very clear.
Wu Li：
Did you try it here before you took it home?
Ma Gang：
Yes.
It was all right.
But when it got to my office, it didn't work properly.
Wu Li：
It's unreasonable.
Ma Gang：
Can you replace it with another one?
Wu Li：
I'm afraid not.
Would you send the computer in and we have it checked first?
Then we'll see what we can do about it.
unit18-3.----------
Title：3.Tom and Susan are in Tom's sports car. They are at a petrol station.
Question：How much does 3 gallons of super cost?
Question：What's the relationship between Tom and Susan?
Question：How does the car work?
Man：Tom
Man：Attendant
Woman：Susan
Tom：
Three gallons of super, please.
Attendant：
Three gallons of super.
Yes, sir.
Susan：
Tom...why don't we get a small family car?
Tom：
What?
You mean, sell my sports car?
Never!
Susan：
But it's expensive to run and it's old.
You bought it long before.
Attendant：
Er...Excuse me.
That's $5, sir.
Tom：
Here you are.
Oh, and would you check my battery, please?
Attendant：
Check the battery, sir?
Certainly.
Susan：
Don't you remember?
It broke down just before we got married and it was in the garage for a whole week!
Tom：
This is a wonderful car!
It always starts first time!
Attendant：
The battery's all right, sir.
Tom：
Thank you.
Susan：
It didn't start first time yesterday morning!
Tom：
That was only because it was so cold!
It's a wonderful engine.
Just listen to it when I start it now!
(Presses starter.
Sound of engine turning over but not starting.)
Susan：
I'm listening, Tom.
unit18-4.----------
Title：4.The following monologue is about mosquitoes.
Question：Do all mosquitoes drink blood?
Question：What is the blood used for?
Question：How does the mosquito grow?
Question：Will the organisms that cause disease affect mosquitoes?
Woman：Mary
Mary：
Mosquitoes are very small insects.
There are more than 2 000 different kinds of mosquitoes.
Female mosquitoes bite people to drink their blood.
Male mosquitoes do not drink blood.
They drink fluids from plants.
The female mosquito uses its long thin sucking tube to break the skin and find blood.
The insect injects the victim with a substance that keeps blood flowing.
The female mosquito drinks the blood and uses it to produce eggs.
One meal gives her enough blood to produce as many as 250 eggs.
The mosquito lays them in any standing water.
The eggs produce worm-like creatures in 2 days to a few months.
However, some eggs can stay in water for years until conditions are right for development.
The worm-like creatures feed on organisms in the water.
After 4 to 10 days, they change again, into creatures called pupas.
The pupas rise to the surface of the water.
Adult mosquitoes pull themselves out of the pupas and fly away.
Mosquitoes can carry organisms that cause disease, but the disease does not affect mosquitoes.
Experts have learned many things about mosquitoes.
For example, the mosquitoes can smell carbon dioxide in the breath of a person or animal from as far away as 60 meters.
Mosquitoes often like the blood of animals better than the blood of people.
Mosquitoes like dark colors.
Many kinds of mosquitoes are the most active in the early morning and early at night.
They eat mostly at night.
unit18-5.----------
Title：Electricity
Woman：Mary
Mary：
If you were thirsty, and took a cup to the kitchen sink, you might first turn the tap on just a little way, so that only a thin stream of water came from it.
Then you would turn the tap a bit further.
Not only would there be more water, but also it would come out with greater force.
If you turned it on as far as it would go, you would get no water in your cup at all, for it would come from the tap in so powerful a jet that it would bounce strai
ght out of the cup again, and most likely drench you.
Mary：
In that stream of water, then, are three things-or rather, two things and their result.
Firstly, the amount or quantity, or current of water.
Secondly, the pressure pushing it.
And thirdly, the power of the jet, which is the result, or product of the current of water and the force pushing it.
Mary：
ELECTRICAL POWER
Mary：
Although this is not quite the same as in electricity, it helps in understanding amps, volts and watts.
For the volt is the unit of electrical pressure, or force.
The amp (short for ampere)is the unit of electrical current, while the watt is the unit of electrical power.
Mary：
A watt is the power given by an ampere of current flowing in a circuit at a pressure of one volt.
So the more the volts and amps there are, the more watts.
As in that water tap, the more current there is, and the more pressure, then the greater the resulting power.
Mary：
The word"pressure"is not quite correct, however, when used about volts.
They are better described as units of force scientists and engineers call them units of "electromotive force", or E.M.F.
Mary：
RESISTANCE
Mary：
When you pump up your bicycle tyre, you use force, or pressure, to push air into the inner tube.
But the air in there already pushes back against you.
Mary：
In much the same way, when you push a current of electricity through a wire, there is a kind of push-back, called "resistance", set up by the metal of which the wire is made.
Mary：
Just as the units of force, current and power have names, so has the unit of electrical resistance.
It is called the "ohm".
Mary：
RESISTANCE OF METALS Mary：
Every metal has its own resistance to the passage of an electrical current through it.
The lower the resistance of a metal, the better it is as a carrier, or "conductor" of electrical energy.
For if you have to use up power in overcoming this resistance, there is so much the less for you at the other end of the conductor.
Mary：
The length of pieces of wire of the same diameter, each piece having a resistance of one ohm,will depend on the metal of which they are made.
Again, for the same diameter, a wire of low resistance will be longer than one of high resistance.
A copper wire will be longer than one of iron, or lead, or nickel, for its resistance is very low, and not much energy is needed to overcome it.
Mary：
For this reason copper is used in making wires, cables and overhead lines for carrying electrical current.
Mary：
Aluminium is another good conductor with a low resistance.
Being light in weight, it is often used for overhead lines, such as you see slung in graceful curves between pylons, but being a soft metal it usually has a steel wire core to give it strength.
Mary：
Sometimes, however, wires of high resistance are put to special uses.
When electrical energy is taken up in overcoming t
he resistance of a wire, it produces heat.
This makes the wire red-hot, as in an electric radiator, or white-hot, as in the filament of a lamp.
Mary：
Thus from metals of high resistance, we can get either heat or light for our use.