听力原文：W: Hello? May I speak to Bill Johns? M: Hi, Amy. This is Bill． W: Oh, hi, Bill. You weren't in engineering class today, were you? M: No, I wasn't．(20)I have a flu. I was wondering if you could tell me what went on. W: I'm sorry that you are ill. Actually we had an interesting class. (19)Dr, Collin talked about a new type of fuel, M: Oh, yeah? Tell me more about it. W: Uh-hum. It's called 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 says something about its exhausts being clear, that it doesn't release as much pollutants as diesel fuel. He mentioned something about DME being more efficient than other alternative fuels. M: When will it replace diesel fuel? W: Not for a while. It's not economical to mass-produce. But it may happen in the future. After all, time will tell. M: Well, thanks for the information. (21)I guess I won't need to borrow your notes. W: (21)Well, maybe you should look at them. We are having a test next week. You have to prepare for it. M: Okay, could you give them to Mike Andrews? I think be is in your psychology class. He is my roommate. W: Sure, I hope you're feeling better soon. M: Thanks. Me too. Bye! (20)