填空题

Some experts believe that, if not for the cultural changes that Africa has experienced, the AIDS virus would not have spread to its present extent.

【参考答案】

Y

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填空题

Some rural African were infected with AIDS because they were given injections of Koprowski’s vaccine.

填空题

Among the theories to explain the origin of AIDS, the polio vaccine theory, in the opinion of the author of the article, seems to be the most plausible one.