A、Pollution problem. B、Population problem. C、Unemployment problem. D、Nuclear weapon problem. D细节题。谈话开始，男士说Are you going to the d

M: Are you going to the demonstration to help stop the spread of nuclear weapons tomorrow?
W: No, Simon. I hate demonstrations. I have heard the police will be standing by with tear gas. I don’t want to get involved in a riot. Besides, I don’t see why the United States should be the only country allowed nuclear weapons.
M: Yes, but North Korea boasting it has nuclear arms is scary. Nobody knows who has and who doesn’t have nuclear arms anymore. There are too many crazy people in the world. Someone has to put a stop to nuclear weapons to save the world from either a bad accident or bad people or terrorists.
W: One hundred ninety countries have signed the Nuclear Non-Proliferation Treaty but the issues are just too complex. There are two sides to every story. I don’t understand it and I have no intention of going to a demonstration. Demonstrations don’t seem to accomplish anything anyway.
M: Several demonstrations have changed politicians’ minds throughout history. As a responsible citizen I think it is important to stand up for what you believe in.
W: Leave it to someone else. As I said, if you listen to both sides of the story, both sides have some good points. I am not an expert on world affairs. Why should I demonstrate and risk getting hurt for something that I am not even sure is right?
M: You are not likely to get hurt. This will be a peaceful demonstration. I have spoken to the organizer for the university group. He has ordered 25 buses to take students downtown. He insists that this will be peaceful. He advocates if you want world peace, peace begins at home—and that means right here in this city. He has asked everyone to be calm. Placards and signs are being prepared for us to carry, but he is insisting students just march, not get angry or confrontational.
W: You go if you want to, Simon, but I plan to study for my physics exam.
M: It would only take two hours of your day. The bus leaves the campus at 11:30 and leaves downtown to return to campus at 12:45. You could eat your lunch on the bus.
W: I am not going, Simon. Why don’t you ask the students in your political science class this afternoon if they want to go?
M: They are all going. We discussed weapons of mass destruction and the Nuclear Non-Proliferation Treaty in our last tutorial. The decision about attending the demonstration was unanimous. All 26 of us decided we definitely wanted to go. Some students are making placards and banners tonight. I am not sure I will be able to help them as I need to study for that physics exam too.
W: It is interesting that your whole political science class is going to the demonstration. Do you have a very persuasive leader in the class?
M: There are a few outspoken people who can present a good argument, but I think most people had already made their mind up to attend before the discussion. There are a lot of pacifists in the group but even the more conservative students are keen to go to this demonstration.
W: Okay, Simon. I need to meet my sister for coffee now.
M: Bye. See you in physics class tomorrow.
Questions:
19. What issue is the demonstration about?
20. Why does the woman say "Demonstrations don’t seem to accomplish anything anyway. "?
21. Why does the woman say "Do you have a very persuasive leader in the class"?