听力原文：M: Hello, professor Johnson. W: Hello, Tony. So what shall we work on today? M: Well, the problem is that this writing assignment isn't coming out right. What I thought I was writing on was to talk about what a particular sport means to me when I participate in. W: What sport did you choose? M: I decided to write about cross-country skiing. W: What are you going to say about skiing? M: That's the problem. I thought I would write about how peaceful it is to be out in the country. W: So why is that a problem? M: I'd like to start describing how quiet it is to be out in the woods. I keep mentioning how much effort it takes to keep going. Cross-country skiing isn't as easy as some people think. It takes a lot of energy, but that's not part of my paper, so I guess I should leave it out. But now I don't know how to explain that feeling of peacefulness without explaining how hard you have to work for it. It all fits together. It's not like just sitting down somewhere and watching the clouds roll by. That's different. W: Then you'll have to include that in your point. The peacefulness of cross-country skiing is the kind you earn by effort. Why leave that out? Part of your point you knew beforehand, but part you discovered as you wrote. That's common, right? M: Yeah, I guess so. Questions: 19. What is the topic of the man's writing assignment? 20. What problem does the man have while working on his paper? 21. What does the woman say is common in writing papers? (20)