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A Biological
Clock{{/B}} Every living thing has what scientists call a biological clock that controls behavior. The biological clock{{U}} (1) {{/U}}plants when to form flowers and when the flowers should open. It tells insects when to{{U}} (2) {{/U}}the protective cocoon (防护卵袋) and fly away, and it tells animals and human beings when to eat, sleep and wake. Events outside the plant and animals{{U}} (3) {{/U}}the action of some biological clocks. Scientists recently found, for example, that a tiny animal changes the color of its fur because of the{{U}} (4) {{/U}}of hours of daylight. In the short{{U}} (5) {{/U}}of winter, its fur becomes white. The fur becomes gray brown in{{U}} (6) {{/U}}in the longer hours of daylight in summer. B. leave C. escape D. enter 更多"阅读下面的短文，文中有15处空白，每处空白给出了4个选项，清根据短文的"的相关试题: [单项选择] 阅读下面的短文，文中有15处空白，每处空白给出了4个选项，清根据短文的内容从4个选项中选择1个最佳答案。
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