51.The U.S.achieved its predominance after World War Ⅱbecause_____ .
［A］it had made painstaking efforts towards this goal
［B］its domestic market was eight times larger than before
［C］the war had destroyed the economies of most potential competitors
［D］the unparalleled size of its workforce had given an impetus to its economy
52.The loss of U.S. predominance in the world economy in the 1980s is manifested in the fact that the American_____ .
［A］TV industry had withdrawn to its domestic market
［B］semiconductor industry had been taken over by foreign enterprises
［C］machine-tool industry had collapsed after suicidal actions
［D］auto industry had lost part of its domestic market
53.What can be inferred from the passage?
［A］It is human nature to shift between self-doubt and blind pried.
［B］Intense competition may contribute to economic progress.
［C］The revival of the economy depends on international cooperation.
［D］A long history of success may pave the way for further development.
54.The author seems to believe the revival of the U.S. economy in the 1990s can be attributed to the____ .
［A］turning of the business cycle
［B］restructuring of industry
［C］improved business management
［D］success in education
Passage 2
Being a man has always been dangerous. There are about 105 males born for every 100 females, but this ratio drops to near balance at the age of maturity, and among 70-year-olds there are twice as many women as men. But the great universal of male mortality is being changed. Now, by babies survive almost as well as girls do. This means that, for the first time, there will be an excess of boys in those crucial years when the are searching for a mate. More important, another chance for natural selection has been removed. Fifty years ago, the chance of a baby(particularly a boy baby)surviving depended on its weight. A kilogram too light or too heavy meant almost certain death. Today it makes almost no difference. Since much of the variation is due to genes one more agent of evolution has gone.
There is another way to commit evolutionary suicide: stay alive, but have fewer children. Few people are as fertile as in the past. Except in some religious communities, very few women has 15 children. Nowadays the number of births, like the age of death, has become average. Most of us have roughly the same number of offspring. Again, differ
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