2. 外语
  3. Life near the shore everywhere is affected by the tides, which come and go twice each day in a cycle of about twelve-and-a-half

Life near the shore everywhere is affected by the tides, which come and go twice each day in a cycle of about twelve-and-a-half

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问题     Life near the shore everywhere is affected by the tides, which come and go twice each day in a cycle of about twelve-and-a-half hours—just different enough from the daily cycle of the sun so that there can be no regular relationship between the shore being alternately wet and dry and alternately light and dark. The extent of the tides varies greatly, from as little as one foot in inland seas like the Mediterranean, to fifty feet or so in the Bay of Fundy in Nova Scotia. In some parts of the world, one of the two daily tides rises higher and falls lower than the other; and tides at the time of new moon and full moon are generally greater than at other times. The extent of the intertidal zone thus varies from day to day as well as from place to place.
    The kinds of organisms living in the region between the tidal limits depend very much on whether the shore is rocky, sandy, or muddy. Rocky shores have the most obviously rich faunas (某地区所有的动物)，because of the firm anchorage for both animals and plants, and because of the small pools left by the retreating seas. Sandy shores, especially when exposed to surf (as they usually are), have the fewest kinds of animals.
The two tides in a given day______.
选项 A、never vary in extent
B、may vary in extent
C、only vary in extent at the time of a new moon or a full moon
D、always vary in extent
答案B
解析 文中第一段第三句说：“在世界一些地方，一天中两次潮汐中的一次会比另一次上涨得高一些，而回落得低一些。”由此可知，在给定的一天中两次潮汐在规模上也许会有变化。
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