听力原文：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. Is your car in the shop? W: No. I've just been thinking a lot about the environment lately. I think the air will be a lot cleaner if we all use public transportation when we could. M: You are right. The diesel bus isn't exactly pollution free. W: True. But they'll be running a lot cleaner soon. We were just talking about that in my environmental engineering class. M: What's the city going to do? Install pollution filters in the buses? W: They could, but those filters make the engines work harder and really cut down on fuel efficiency. Instead they found a way to make their engines more efficient. M: How? W: Well, there is a material called the coniine oxide. It's a really good insulator. And a thick coat of it gets sprayed on the certain part of the engine. M: An insulator? W: Yeah. Actually, what it does is to reflect back the heat of burning fuel. So the fuel will bum more completely. M: Sounds like people should all go out and get this stuff to spray their car engines. W: Well, it's not really that easy. You first have to heat the material over 10,000 degrees and then, well, you get the idea. It's not something you or I can do ourselves. (27)