单选题 The United States population is growing older. In 1987, 12 percent of Americans were 65 years old or older, compared with 8 percent in 1950. Population experts at the U.S. Bureau of the Census expect this percentage to continue to rise gradually, reaching 14 percent in 2010, then to skyrocket during the next 20 years, reaching 21 percent by 2030. This "graying of America" has generated concerns about whether the best really is yet to be, about how well off tomorrow's elderly will be. There also are questions about the impact of an aging population on the rest of society.
The graying of America has two causes. First, advances in medical care have enable people to live longer. In the United States in 1900, the average life expectancy at birth was 47.7 years. By 1985, the latest year for which figures are available, it has climbed to 74.7 years.
Second, the U.S. birthrate rose in the mid-1900s, interrupting a long, slow decline. A dramatic increase occurred during this brief rise. From 1945 to 1947, the rate jumped from 20.4 births for every 1,000 people to 26.6. In 1957, the birthrate was still high — 25.3 — but then began to decline. The birthrate dropped to the 1933 level of 18.4 in 1966, andby 1985, was 15.7. Most experts see little change in the downward trend of the birthrate in the foreseeable future.

单选题 What is the author's main purpose in the passage?
A. To bring attention to the needs of the elderly.
B. To contrast birth rates and life expectancy rates.
C. To explain how and why the American population is aging.
D. To show the percentages of age groups in general population.
【正确答案】 A
【答案解析】[解析] 主旨大意题。需要通读全文，了解每段讲什么，再结合到一起看，第一段主要说美国出现老龄化现象，并且提出了the graying of America，第二、三段主要说明了the graying of America出现的原因，大家可能会误选C项，它是文章的大意，并不是作者的目的，对比而言，A项更贴题意。
单选题 During which period of time will the percentage of Americans 65 years old or older increase the most?
A. 1970-1990. B. 1990-2010. C. 2010-2030. D. 2030-2050.
【正确答案】 C
【答案解析】[解析] 判断推理题。从文章的第一段In 1987...by 2030可知答案选C。
单选题 In the first paragraph, the phrase "this graying of America" refers to ______.
A. the uncertainty of the future for older Americans
B. the effects of population on the health of the elderly
C. statistics released by the U.S. Bureau of the Census
D. the increasing number of elderly people in the population
【正确答案】 B
【答案解析】[解析] 事实细节题。根据文章的第一段的倒数第二句this graying of America has...about how well off tomorrow's elderly will be，关于怎么样能使未来的老人更健康，更富有，所以答案选B。
单选题 About how long did it take the birthrate to return to the 1933 level?
A. 20 years. B. 30 years. C. 40 years. D. 50 years.
【正确答案】 B
【答案解析】[解析] 判断推理题。根据文章的第三段第一句话the U.S. birthrate rose in the mid-1900s...slow decline，还有这段的第五句The birthrate dropped to the 1933 level...，将两个年份相减，大概就是30年，所以答案选B。
单选题 Which of the following conclusions about the birthrate is supported by the passage?
A. The long-range decline in the birthrate will continue in the next century.
B. Another dramatic increase in the birthrate will occur before the 21st century.
C. The birthrate will continue to vary greatly.
D. An increase in the birthrate depends mainly on advances in medical care.
【正确答案】 B
【答案解析】[解析] 判断推理题。从文章的最后一句Most experts see little change in the downward trend of the birthrate in the foreseeable future得知答案选B。