听力原文：W: Hello? M: Hi, Mary, this is Bill Johnson. W: Oh hi, Bill. 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. Dr. Kelvin talked about a new type of fuel. M: Oh, yeah? W: Uh-hum. It's called dimethylether or DME. M: Oh, I remember reading something about DME, but I don't remember the chemical terminology. 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. Kelvin said something about its exhausts being clear, that 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 can 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 Bill Stanford? I think he is in your psychology class. He is my roommate. W: Sure. I hope you're feeling better soon. M: Thanks. Me, too. Bye! W: Bye! (23)