题干

如图所示,在柱形容器中装有部分水,容器上方有一可自由移动的活塞。容器水面浮有一个木块和一个一端封闭、开口向下的玻璃管,玻璃管中有部分空气,系统稳定时,玻璃管内空气柱在管外水面上方的长度为a,空气柱在管外水面下方的长度为b,水面上方木块的高度为c,水面下方木块的高度为d。现在活塞上方施加竖直向下、且缓缓增大的力F,使活塞下降一小段距离(未碰及玻璃管和木块),下列说法中正确的是            (      )

A:d和b都减小

B:只有b减小

C:只有a减小

D:a和c都减小

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答案(点此获取答案解析)

C

同类题5

阅读理解

    Having experienced a shocking electrical accident, which caused him to become both blind and deaf, James Franco's world became completely dark and quiet for almost ten years. The loss of sight and hearing threw him into such sorrow that he tried a few times to put an end to his life. His family, especially his wife, did their best to tend and comfort him and finally he regained the will to live.

    One hot summer afternoon, he was taking a walk with a stick near his house when a thunderstorm started all at once. He stood under a large tree to avoid getting wet, but he was struck by lightning. Witnesses (目击者) thought he was dead but he woke up 20 minutes later, lying face down in muddy water. He was trembling badly, but when he opened his eyes, he could hardly believe what he saw: a tree and a muddy road. When Mrs. Franco came running up to him, shouting to their neighbors to call for help, he could see her and hear her voice for the first time in nearly ten years.

    The news of James regaining his sight and hearing quickly spread and many doctors came to examine him. Most of them said that he regained his sight and hearing from the shock he got from lightning. However, none of them could give a compelling answer as to why this should happen. The only reasonable explanation given by one doctor was that, since James lost his sight and hearing as a result of a sudden shock, perhaps, the only way for him to regain them was by another sudden shock.