Now you’ll hear two long conversations.

　　Conversation One

　　W:OK, last night you were supposed to read an article about human bones. Are there any comments about it?

　　M:Well, to begin with, I was surprised to find out there was so much going on in bones. I always assumed they were pretty lifeless.

　　W:Well, that’s an assumption many people make. But the fact is bones are made of dynamic living tissue that requires continuous maintenance and repair.

　　M:Right. That’s one of the things I found so fascinating about the article the way the bones repair themselves.

　　W:OK. So can you tell us how the bones repair themselves?

　　M:Sure. See, there are two groups of different types of specialized cells in the bone that work together to do it. The first group goes to an area of the bone that needs repair. This group of cells produces the chemical that actually breaks down the bone tissue, and leaves a hole in it. After that the second group of specialized cells comes and produces the new tissue that fills in the hole that was made by the first group.

　　W:Very good. This is a very complex process. In fact, the scientists who study human bones don’t completely understand it yet. They are still trying to find out how it all actually works. Specifically, because sometimes after the first group of cells leaves a hole in the bone tissue, for some reason, the second group doesn’t completely fill in the hole. And this can cause real problems. It can actually lead to a disease in which the bone becomes weak and is easily broken.

　　M:OK, I get it. So if the scientists can figure out what makes the specialized cells work, maybe they can find a way to make sure the second group of cells completely fills the hole in the bone tissue every time. That’ll prevent the disease from ever occurring.

　　Questions 19 to 22 are based on the conversation you have just heard.

　　19.What is the discussion mainly about?

　　【解析】[C]對話一開始就談論人類骨骼的問題，女士說 But the fact is bones are made of dynamic living tissue that requires continuous maintenance and repair. 后面的對話都是針對這個話題展開的討論，可見整個對話討論的話題是骨骼的自我修復能力。

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

　　【解析】[C]男士解釋了第一組細胞的作用，第一組細胞生成一種化學物質分解骨組織(This group of cells produces the chemical that actually breaks down the bone tissue...)，由此可見答案是They break down bone tissue.

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

　　【解析】[B]女士說這種特殊細胞作用于人類骨骼的過程相當復雜，事實上，連研究人類骨骼的科學家都不能完全了解這個過程。從這一句中可以知道：In fact, the scientists who study human bones don’t completely understand it yet. 所以答案即是這些科學家也不完全知道這些細胞如何工作。

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

　　【解析】[A]學習這些人類骨骼中的特殊細胞的重要目的是為了學習如何預防骨頭疾病。從男士的這一句話中可看出：That’ll prevent the disease from ever occurring. 這樣可以在疾病發生之前預防疾病，可見[A]符合題意。

　　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:Yeah. 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 10,000 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]女士說為了環保應該多乘坐公共交通設備，因此之后的話題便圍繞如何節能保護環境的問題展開。這段對話主要討論的是公共汽車的節能問題，討論了如何讓公共汽車燃料更有效的利用，因此[C]符合題意。

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

　　【解析】[B]對話開頭部分就交代了此題答案，那位女士說她不開自己的車而乘坐公共汽車是為了降低環境污染。從她提到的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]這種新的材料是在引擎部位噴灑的一種絕緣材料。從女士的話中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。這種材料的用途是將燃料燃燒的熱量反射回去，從而達到提高效率的結果。

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