20. What is the function of the first group of specialized cells discussed in the talk?

C士细茫细一只学史纸织(This group of cells produces the chemical that actually breaks down the bone tissue)纱丝杉They break down bone tissue.

21. What does the professor say about scientists who study the specialized cells in human bones?

B女士说细头墓嗟庇Ｊ迪Ｐ就纺垦б度�私獭一锌知In fact, the scientists who study human bones dont completely understand it yet. 源鸢讣些学也知些细喂

22. According to the student, what is one important purpose of studying specialized cells in human bones?

A学习些头械细要目为学习预头士一浠靶可縏hatll prevent the disease from ever occurring. 诩之前预杉A莘狻�

Conversation Two

M: Hi Diana, mind if I sit down?

W: Not at all, Jerry. How have you been?

M: Good. But Im surprised to see you on the city bus. Your car in the shop?

W: No. Ive just been thinking a lot about the environment lately. So I decided the air will be a lot cleaner if we all use public transportation when we could.

M: Im sure you are right. The diesel bus isnt exactly pollution free.

W: True. Theyll be running a lot cleaner soon. We were just talking about that in my environmental engineering class.

M: What could the city do? Install pollution filters in all their buses?

W: They could, but those filters make the engines work harder and really cut down on the fuel efficiency. Instead they found a way to make their engines more efficient.

M: How?

W: Well, there is a material thats a really good insulator. And a thin coat of it gets sprayed on the certain part of the engine.

M: An insulator?

W:Y eah. What it does is reflect back the heat of burning fuel. So the fuel will burn much hotter and burn up more completely.

M: So a lot less unburned fuel comes out to pollute the air.

W: And the bus will need less fuel. So with the saving on fuel cost, they say this will all pay for itself in just six months.

M: Sounds like people should all go out and get some this stuff to spray their car engines.

W: Well, its not really that easy. You see, normally, the materials are fine powder. To melt it so you can spray a coat of it on the engine parts, you first have to heat it over 10000 degrees and then, well, you get the idea. Its not something you or I will be able to do ourselves.

Questions 23 to 25 are based on the conversation you have just heard.

23. What is the conversation mainly about?

C女士说为嘶应枚通璞钢�幕围谓鼙展味曰要鄣枪慕猓�霉燃细效茫耍C莘狻�

24. Why did the woman decide to ride the city bus?

B荻曰头志徒舜鸢福位女士说约某贸斯为私突染岬絊o I decided the air will be a lot cleaner if we all use public transportation when we could 傻知

25. What is the new material?

D 碌牟娌课灰恢驹迪∨�士幕there is a material thats a really good insulator. And a thin coat of it gets sprayed on the certain part of the engine傻贸植系途墙燃燃盏去佣锏叫�实慕

Section  B

Passage One

A guide dog is a dog especially trained to guide a blind person. Dogs chosen for such training must show good intelligence, physical fitness, and responsibility.

At the age of about fourteen months, a guide dog begins an intensive course that lasts from three to five months. It becomes accustomed to the leather harness and stiff leather handle it will wear when guiding its blind owner. The dog learns to watch traffic and to cross streets safely. It also learns to obey any command that might lead its owner into danger.

The most important part of the training course is a fourweek program in which the guide dog and its future owner learn to work together. However, many blind people are unsuited by personality to work dogs. Only about a tenth of the blind find a guide dog useful.
Questions 26 to 28 are based on the passage you have just heard.

26. How long does the intensive course last?

A确岬絘n intensive course that lasts from three to five months确为 A荨

27.Which of the following is not a necessary skill guide dogs have to learn?

D荽The dog learns to watch traffic and to cross streets safely. It also learns to obey any command that might lead its owner into danger. 锌煽也诘盲犬训围诘募堋

28.How long does the most important training course last?

C要训纬坛堋确指吮鸢浮The most important part of the training course is a fourweek program哟司屑煽

Passage Two

People dreams four to six times a night. They dream while they are in the REM stage of sleep, which means rapid eye movement stage in ones sleep. Sleepers go into the REM stage about every 90 minutes. The first dream of the night may last about ten minutes. Each dream gets a little longer. The last dream of the night may be an hour long.

People need their dreams. Younger children spend more time dreaming. Babies spend almost half of their sleep in the REM stage.

One experiment showed that everyone needs to dream. Doctors gave some people sleeping pills. These sleeping pills didnt let them going to REM sleep. After a few nights without dreams, they began to feel bad. They became angry easily, they worried a lot, and they wanted to fight with everyone. Then they stopped taking the sleeping pills. They all began to dream all night for a few nights to catch up.

Why do people dream? Dreams give them time to find the answers to some of their problems. If they think they will have difficult problems the next day, they may spend more time on REM sleep the night before. In their dreams, they may find an answer to their problems.

Questions 29 to 31 are based on the passage you have just heard.