A、Eleven dollars for the event. B、One dollar for the event. C、30 cents per mile. D、25 cents per mile. D数字题。浏览选项可知，题目和钱的数目有关。对话中，

W: Hey, Joe, haven’t seen you for months. Care for a drink at the bar?
M: I’d love to, but I’m already late for the talk about the benefits of walkathon this weekend.
W: Walkathon? What’s all this about?
M: Don’t you know? Most of the residents in Packer Hall are going to try to walk the seven miles from the engineering library, across campus and down to city hall, in an effort to raise money for the new children’s hospital.
W: Sounds like a good idea. But I don’t understand where the money comes from.
M: Well, a few days before the walkathon, each participant goes around asking people to pledge just a certain amount of money for each mile that he or she expects to walk in the event. Then after the walkathon’s over, the participants go back to those same people, collect the money pledged and send it into the hospital.
W: So you mean if someone pledges, say, a dollar a mile, and you walk five miles, you can get five dollars?
M: That’s right. Of course, most of my friends aren’t such big spenders; the biggest pledge I’ve gotten so far is 25 cents a mile.
W: And how many people have made pledges for you?
M: Eleven so far. Say, how about making it an even dozen?
W: Sure. If you do the same for me. The walkathon sounds like a perfect opportunity for me to break in my new pair of sports shoes.
Questions 19 to 22 are based on the conversation you have just heard.
19. Who is going to participate in the walkathon?
20. What can we learn about the course of the walkathon from the conversation?
21. What will happen to the money raised at the walkathon?
22. How much is the maximum pledge Joe has gotten from his friends?