听力原文：W: Hi, Mike. M: Hi. I'm surprised to see you on the city bus. Why not drive your car? W: (23) I've been thinking about the environment lately. If we all use public transportation when we could, the air will be much cleaner. M: Right. But the 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 of some sort on their 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: (24) Well, there is a material called the confine 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: (25) Yes. It reflects back the heat of burning fuel. So the fuel will burn much more hotly and burn up more completely. M: So a lot less unburned fuel comes out to pollute the air, right? W: (25) Yeah, and the bus will need less fuel. So with the savings 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 this stuff to spray their car engines. W: Well, not really that easy. To melt the materials before you can spray a coat of it on the engine parts, you first have to heat it over 10,000 degrees. It's not something we are able to do ourselves. 23. Why doesn't the woman drive her car? 24.What are the two speakers talking about? 25.What can we learn from the conversation about the material mentioned? (20)