题目

Today most Chinese teenagers are happy to be favored by two parents and four grandparents in their families. But have you ever thought about how to take care of four to twelve old people when you grow up and get married? This could be a problem for most Chinese youths as China is entering a new stage of an aging society. An aging society refers to one where 10 percent or more of its population is over 60. By the end of 2007, Chinese over 60 years old have made up 11.7 percent of the nation’s total population. “China is getting old before becoming rich,” said Cai Chuang, a professor如果命题对成立，那么它对也成立，又若对成立，则下列结论正确的是（    ） A．对所有自然数成立 B．对所有正偶数成立 C．对所有正奇数成立 D．对所有大于1的自然数成立