听力原文：M: Hi Diana, mind if I sit down? W: Not at all, Jack. 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. 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 gonna do? Install pollution filters of some sort on their buses? W: They could, but those filters make the engines work harder and really cut down on fuel efficiency. In stead they found a way to make their engines more efficient. M: How? W: Well, there is a material called coniine oxide. It's a really good insulator. And a thick coat of it get sprayed on certain part of the engine. M: An insulator? W: Well, yeah. Actually, 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, right? W: Yeah, and the bus will need less fuel. So with the savings on fuel oil costs, they say this will all pay for itself in just six months. M: Sounds like people should all go out and get some of this stuff to spray on 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 would be a ble to do ourselves. (23)