America is growing older. Fifty - eight years ago, only 4 out of every 100 people in the United States were 10 or older. To day, 10 out of every 100 Americans are over 10. The aging of the population will affect（影响）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（行为） is suitable（合适）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 kept us on time and told 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 15 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 surprise at older people who act in youthful ways.
12．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
13．The underlined word “one”refers to ________ .
A. a society　　　B. America      C. a place　　　　D. population
14．” Act your age” means people should ________ .
A. be active when they are old
B. do the right thing at the right age
C. show respect for their parents young or old
D. take more physical exercise suitable to their age
15．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

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