2002年5月托福聽(tīng)力文字

　　2002年5月托福聽(tīng)力文字

　　Part B

　　31－34

　　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 were 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 produce 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 produce 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 every occurring.35－38M： 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 call 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 called XXX. It‘s a really good insulator. And a think coat of it get 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 unburning 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 be able to do ourselves.