A、A fuel that burns cleanly. B、An oil additive that helps cool engines. C、A material from which filters are made. D、An insulatin

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.