听力原文：M: Today so many people are talking about AIDS. Is the AIDS epidemic very serious

W: Oh, yeah. To say the impact on our society, this disease will be the most serious public-health problem we are facing now. On a global scale, it threatens to undermine countries, especially in Africa.

M: Oh, it's so terrible？ What do you mean by "undermine countries"？

W: It is a very serious disease in the middle ages of the population, so that it will greatly reduce the number of people carrying out the functions of the society. In parts of Africa, it's happening already.

M: We know that AIDS is mainly caused by sex contact and blood exchange or drug abuse. Do you think people's basic behavior. can be altered in time to stop the AIDS epidemic？

W: In time to have a significant impact, yes. I don't think we'll be perfect. People will respond differently. But for the homosexual population in San Francisco, the rate of homosexually transmitted diseases fell dramatically when a serious educational program was put in place. People were obviously willing to change their behavior. when they were made to realize how severe a risk they were taking.

M: What about groups not yet hard hit？ Can the message get to them before massive death occurs？

W: It is certainly harder to reach people when they don't see the consequence of what they're doing right around them or when the consequence is extremely delayed.

M: How can we reach people？

W: A massive educational campaign is the only thing conceivable at the moment that can help. To argue that it's difficult and expensive and therefore we shouldn't do it would be self-defeating.

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A．The epidemic of AIDS.

B．The treatment of AIDS.

C．The transmission of AIDS.

D．The impact of AIDS.