What’s the conversation mainly about?

W: Hi, Bill. You weren’t in engineering class today, were you?
M: Hi, Amy. I have the flu. I was wondering if you could tell me what went on.
W: Actually we had an interesting class. Dr. Collin talked about a new type of fuel.
M: Oh, yeah?
W: Uh-hum. It’s called dimethyl ether or DME.
M: Oh, I remember reading something about DME. It’s mostly used in spray cans, right?
W: Right. DME doesn’t destroy the ozone, so it’s been environmentally friendly.
M: But doesn’t DME pollute the air if it’s burned in an engine?
W: Dr. Collin said something about its exhausts being clear, that it doesn’t release as many pollutants as diesel fuel. And he mentioned something about DME being more efficient than other alternative fuels.
M: So when will it replace diesel fuel?
W: Not for a while. It’s not economical to mass-produce.
M: Well, thanks for the information. I guess I won’t need to borrow your notes.
W: Well, maybe you should look at them. We are having a test next week.
M: Okay, could you give them to Mike Andrews? I think he is in your psychology class. He is my roommate.
W: Sure. I hope you’re feeling better soon.
M: Thank you.