A、It makes the fuel burn more efficiently. B、It helps release more unburned fuel. C、It is easy to install. D、It is very cheap. A

M: Hi, Diana. 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 transport when we could.
M: I’m sure you are right. The diesel bus isn’t exactly pollution free.
W: True. They’ll be running a lot cleaner soon. We were .just talking about that in my environmental engineering class.
M: What could the city do? Install pollution filters in all their buses?
W: They could, but those filters make the engines work harder and really cut down on the fuel efficiency. Instead, they found a way to make their engines more efficient.
M: How?
W: Well, there is a new insulator. And you spray a thick coat of it on the engine.
M: An insulator?
W: Yeah. 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.
W: And the bus will need less fuel. So with the saving on fuel cost, they say this will all pay for itself in just six months.
19. Why does Diana take a bus that day?
20. What is true about Diana?
21. What justifies the installation of a new insulator in the buses according to Diana?
22. What is the major concern of the woman?