A man steps on what seems like solid ground but discovers with horror that the ground is giv ing 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 giv ing 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 treach erous (不可信的) earth The solid ground was solid only in【B2】______.It was actually quick sand, 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.
【B4】

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答案grains

解析 根据谓语are,此处需要可数名词复数形式,grains of sand表示“沙粒”。
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