问题
单项选择题
运料工用绞车运料过程中，车辆速度（）。
A.可根据地形调整
B.保持最高速度
C.尽量匀速行驶
D.可以忽快忽慢
答案
参考答案：C
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运料工用绞车运料过程中，车辆速度（）。
A.可根据地形调整
B.保持最高速度
C.尽量匀速行驶
D.可以忽快忽慢
参考答案：C
You have often __1__ people talk about work. Perhaps you have __2__ your friends about how hard you worked to get something done. However, you may have done no work __3_ you think you worked hard. A boy is pushing a big box very hard, but the box is __4__ heavy for him to move and he may __5__ to push against the box. __6__ the language of science, he has not done __7__ work. Can you think you are working when you are studying or talking? In science, work is only done when a force(力) moves something that has weight through a distance（距离）. Work =" force" × distance moved. __8_ you want to find out whether work is done, _9_ yourself, “Is a push or a pull moving something through a distance?” If your answer is __10_, then work is being done.
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