21. What does the professor say about scientists who study the specialized cells in human bones?
【解析】[B]女士说这种特殊细胞作用于人类骨头的过程相当复杂，事实上，连研究人类骨头的科学家都不能完全了解这个过程。从这一句中可以知道：In fact, the scientists who study human bones don’t completely understand it yet. 所以答案即是这些科学家也不知道这些细胞如何工作。
22. According to the student, what is one important purpose of studying specialized cells in human bones?
【解析】[A]学习这些人类骨头中的特殊细胞的重要目的是为了学习如何预防骨头疾病。从男士的这一句话中可看出：That’ll prevent the disease from ever occurring. 这样可以在疾病发生之前预防疾病，可见[A]符合题意。
Conversation Two
M: Hi Diana, mind if I sit down?
W: Not at all, Jerry. How have you been?
M: Good. But I’m surprised to see you on the city bus. Your car in the shop?
W: No. I’ve 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: I’m sure you are right. The diesel bus isn’t exactly pollution free.
W: True. They’ll 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 that’s 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, it’s 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. It’s 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?
【解析】[C]女士说为了环保应该多乘坐公共交通设备，因此之后的话题便围绕如何节能保护环境的问题展开。这段对话主要讨论的是公共汽车的节能问题，讨论了如何让公共汽车燃料更有效的利用，因此[C]符合题意。
24. Why did the woman decide to ride the city bus?
【解析】[B]对话开头部分就交代了此题答案，那位女士说她不开自己的车而该乘公车是为了降低环境污染。从她提到的So I decided the air will be a lot cleaner if we all use public transportation when we could 即可得知。
25. What is the new material?
【解析】[D] 这种新的材料是在引擎部位喷洒的一种绝缘材料。从女士的话中there is a material that’s a really good insulator. And a thin coat of it gets sprayed on the certain part of the engine即可得出。这种材料的用途是将燃料燃烧的热量反射回去，从而达到提高效率的结果。
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?
【解析】[A]文中明确提到an intensive course that lasts from three to five months，因此正确答案为 [A]。
27.Which of the following is not a necessary skill guide dogs have to learn?
【解析】[D]答案依据是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. 从这两句中可看出看家不属于导盲犬训练范围内的技能。
28.How long does the most important training course last?
【解析】[C]最重要的训练课程持续四周。文中明确指出了本题答案。The most important part of the training course is a fourweek program，从此句中即可看出。
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 one’s 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 didn’t 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.
29.How often does a person dream each night?
【解析】[B]文章一开始即交待了一个人一晚上要做梦四到六次。从第一句就可看出People dreams four to six times a night.因此，答案为 [B]。
30.What is true according to this passage?
【解析】[D]安眠药会阻止人们进入REM睡眠状态。These sleeping pills didn’t let them going to REM sleep.可看出 [D] 项正确。
相关推荐：2007年12月英语四级考试全真预测试题
更多信息请访问：考试吧四六级栏目
＞＞＞来四六级论坛看看吧
＞＞＞四六级博客圈，你开博了吗？
