The piston slides noiselessly up and down.
这个活塞上下活动,没有响声。
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Then, with another whistle, he began to move forward;the train increased its speed, and soon its rapidity became frightful;a prolonged screech issued from the locomotive; the piston worked up and down twenty strokes to the second.
紧接着响了第二声汽笛,火车又开始前进了。它不断加快速度,一会儿,速度已经大到了十分可怕的程度,车上只能听见机车发出的一阵隆隆声,每秒钟进返二十次。