問題詳情

請回答第 42 題至第 45 題：Real quicksand, the kind that is almost impossible to extricate yourself from, is not just water and sand. Areport in the current issue of Nature shows that salt and clay are also major ingredients.Their study began when Dr. Daniel Bonn, a professor of physics at the University of Amsterdam, was in Irana few years ago and saw signs warning of quicksand. Naturally, the warning prompted him to collect samples andhe sank in to his ankles.He quickly escaped, but even shallow quicksand can be hard to step out of. Back home, Dr. Bonn and hiscolleagues found out why. Sand grains in quicksand are usually loosely packed, with the clay acting as a fragilegel holding the grains together.Hit with sudden force from a hapless victim, the quicksand gel turns to liquid. Then salt causes clay particlesto stick to one another instead of the sand grains, with the result that a victim ends up surrounded by denselypacked sand.The force needed to pull out a person immersed in quicksand is about the same needed to lift a car, Dr. Bonnsaid. The trick for escaping is to slowly wiggle the feet and legs, allowing water to flow in. People float inquicksand so it is also impossible to sink all the way in, but quicksand usually forms at river estuaries, so acaptive could drown at high tide.
42 Which of the following is NOT a major ingredient of quicksand?
(A)water
(B)sand
(C)salt
(D)gel

參考答案

答案：D
難度：適中0.506667
統計：A(45),B(100),C(74),D(228),E(0)

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