2. 外语
  3. The term biological clock is applied to the means by which living things adjust their activity patterns, without any【B1】______ c

The term biological clock is applied to the means by which living things adjust their activity patterns, without any【B1】______ c

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问题     The term biological clock is applied to the means by which living things adjust their activity patterns, without any【B1】______ cue, to the time of day, or the month, or the year. The biological clocks seem to be beautifully【B2】______ the needs of living things. They are affected but little, if at all, by drugs, chemicals, or wide temperature difference —【B3】______ which may alter substantially the rates of all ordinary processes of the body.
    The nature of the biological clocks’【B4】______ is still a mystery. Two quite different theories can【B5】______ them. According to the first of these theories, each individual contains its own independent timing system. This is believed to have【B6】______, aided by natural selection, as an adaptation to the rhythmic environment. It has now become independent of the environment. The other theory holds that living things react【B7】______ to their rhythmic physical environment. The setting of their biological clocks, therefore,【B8】______ a constant adjustment to subtle environment forces. But the search for the【B9】______ timing system has been futile thus far. Not only has no independent timing system ever been discovered, but there has not yet been even a guess【B10】______ its nature.
【B6】
选项
答案evolved
解析 此空需要动词的过去分词，与空格前的have构成完成时态作谓语。evolve“进化，发展”，其过去分词在词尾加-d。
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