2. 外语
  3. There are about 105 males born for every 100 females, but this【B1】______ drops to near balance at the age of maturity, and among

There are about 105 males born for every 100 females, but this【B1】______ drops to near balance at the age of maturity, and among

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问题      There are about 105 males born for every 100 females, but this【B1】______ 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【B2】______ is being changed. Now, boy babies【B3】______ almost as well as girls do. Fifty years ago, the chance of a baby(particularly a boy baby)surviving depended on its weight. A kilogram too light or too heavy【B4】______ almost certain death. Today it makes almost no【B5】______ . Since much of the variation is due to genes, one more agent of evolution has gone.
    There is another way to【B6】______ evolutionary suicide: stay alive, but have fewer children. Few people are as【B7】______ as in the past. Nowadays the number of births, like the age of death, has become  【B8】______ .Again,【B9】______ .
     For us, this means that evolution is over; the biological Utopia has arrived. Strangely, it has involved little physical change. No other species fills so many places in nature.【B10】______ . We did not evolve, because machines and society did it for us. Darwin had a phrase to describe those ignorant of evolution: they "look at an organic being as a savage looks at a ship, as at something wholly beyond his Comprehension." No doubt we will re- member a 20th century way of life beyond comprehension for its ugliness.【B11】______ .
【B1】
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答案ratio
解析 this 表明所填词应是对105males born for every 100 females的归纳概括，其表示的是婴儿出生时的性别比例，故填入ratio“比；比率”。
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