A、The high temperatures required for its use. B、The high cost of materials used in its production. C、The lack of trained environ

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. 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. 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 get sprayed on the 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 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.