A、More than 30. B、Less than 30. C、About 30. D、30 B根据最后一句可知，南非患艾滋病的人的平均寿命为less than 30。

Thembeka is a 12-year-old girl who lives in a rural village of southern Africa. Her parents died of AIDS, and she was left to care for her three little sisters aged ten, six, and four. The girls have no income and rely totally on neighbors’ kindness—a loaf of bread or a few potatoes. A picture of the four orphaned girls was displayed on the front page of a South African newspaper that reported on the 13th International AIDS Conference, held during July in 2000 in Durban, South Africa.
    Millions of AIDS orphans face a situation similar to that of Thembeka and her younger sisters. The conference discussed methods of dealing with the growing AIDS crisis, such as education on the prevention of AIDS through the use of condoms; the use of a less expensive AIDS treatment, which is now available; and more funding for the development of AIDS vaccines.
    Statistics released at the conference were frightening. Every day an estimated 7 000 young people and 1 000 infants are infected with HIV. In one year, 1999, some 860 000 children in sub-Saharan Africa couldn’ t go to school as they had lost their teachers because of AIDS.
    According to a survey published by the Medical Research Council of South Africa, 4. 2 million people in South Africa are infected with HIV, representing 1 out of every 10 citizens. The situation in neighboring countries is worse. It was also reported on an estimate given by the U. S. Census Bureau: " The populations of some AIDS stricken African countries will soon begin to fall as millions die of the disease, and life expectancy by the end of this decade will plunge to less than 30. "
21. How do Thembeka and her sisters live?
22. Where was the picture of the four orphaned girls displayed?
23. Why couldn’ t the 860 000 sub-Saharan children go to school in 1999?
24. According to the survey, what percentage of the population in South Africa has been infected with HIV?
25. What will be the life expectancy of the AIDS people in African countries by the end of this decade?