What is the conversation mainly about?

W: Hello?
M: Hi. Marie. this is Tom Ford.
W: Oh, hi, Tom. You weren’t in engineering class today, were you?
M: I have the flu. I was wondering if you could tell me what went on.
W: Actually we had an interesting class. [7]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 [8]it doesn’t release as much pollutants as diesel fuel. And he mentioned something about DME being more efficient than other alternative fuels.
M: When will it replace diesel fuel?
W: [9]Not for a while. It’s not economical to mass-produce.
M: Well. thanks fur the information. I guess I won’t need to borrow your notes.
W: Well, [10]maybe you should look at them. We are having a test next week.
M: Okay, could you give them to William Johnson? I think he is in your psychology class. He is my roommate.
W: Sure. I hope you’re feeling better soon.
M: Thanks. Bye-bye!
W: Bye!