阅读理解。 America is growing older. Fifty years ago, only 4 out of every 100 people in the United States were 65 or older. Today, 10 out of every 100 Americans are over 65. The aging of the population will affect American society in many ways - education, medicine, and business. Quietly, the graying of America has made us a very different society - one in which people have a quite different idea of what kind of behavior is suitable at various ages. A person's age no longer tells you anything about his/her social position, marriage or health. There's no longer a particular year in which one goes to school or goes to work or gets married or starts a family. The social clock that keeps us on time and tells us when to go to school, get a job, or stop working isn't as strong as it used to be. It doesn't surprise us to hear of a 29-year-old university president or a 35-year-old grandmother, or a 70-year-old man who has become a father for the first time. Public ideas are changing. Many people say,'I am much younger than my mother-or my father-was at my age. 'No one says Act your age' any more. We've stopped looking with surprising at older people who act in youthful ways.' 1. It can be learnt from the text that the aging of the population in America _________. A. has made people feel younger B. has changed people's social position C. has changed people's understanding of age D. has slowed down the country's social development 2. The underlined word 'one' refers to'________.' A. a society B. America C. a place D. population 3. 'Act your age' means people should _________. A. be active when they are old B. do the right things at the right age C. show respect for their parents young or old D. take more physical exercise suitable to their age 4. If a 25-year-old man becomes general manager of a big firm, the writer of the text would most probably consider it _______. A. normal B. wonderful C. unbelievable D. unreasonable