A man steps on what seems like solid ground but discovers with horror that the ground is giving way beneath his feet. The man st

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问题     A man steps on what seems like solid ground but discovers with horror that the ground is giving way beneath his feet. The man struggles【B1】______, but he is mercilessly trapped. He cannot escape. Slowly he sinks deeper and deeper until at last he is gone, buried in the treacherous(不可信的)earth The solid ground was solid only in【B2】______. It was actually quicksand, which is a deep mass of fine sand【B3】______ water.
    How is quicksand formed? Water pushes up from below the surface and is held by the sand. The【B4】______ of sand are forced apart by the water. They cannot hold any weight. The subsurface water may have come from a spring, a river, or a stream. Sometimes pools of water near beaches become filled with sand. When the soil under these pools does not allow for good drainage, the sand can become stretches of quicksand.
    Is it true that a man who steps into quicksand【B5】______ die? No, four men have fought their way from quicksand to firm land again. It is【B6】______ that creates the condition that can【B7】______ death, for the more a person struggles, the worse matters become. Quick movements will make the sand yield【B8】______, but then it rushes and settles solidly around the body.
    A man trapped in quicksand should either【B9】______, or not move at all, except to stretch out his arms. When the weight of the sand his body has【B10】______ equals his weight, he will stop sinking. With feet held still, and slow movements of arms, as in the backstroke in swimming men have managed to roll to safety and reach firm ground.
【B9】

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答案lie back

解析 lie back“仰靠,向后靠”。空格前的should提示此空需用动词原形。
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