题干

如图所示,小华同学酷爱滑板运动.在他玩滑板的过程中,关于几个力学问题的思考,下列说法正确的是(  )

A:玩滑板时尽量降低重心是为了增加板对地的压力

B:人对滑板的压力和滑板对人的支持力是一对平衡力

C:滑板底部安装轮子是为了用滚动代替滑动从而减小摩擦力

D:滑板在地面滑行是因为人和滑板具有惯性,当惯性消失,滑板就停下来

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答案(点此获取答案解析)

C

同类题1

根据短文内容和首字母提示,在下文空格处填入适当的词使短文完整。(每空一词)

    In a tree in a jungle, there once lived many birds. They were  h____ in their small nests(鸟巢) and sang every day. Before the rainy season arrived, all the animals in the jungle repaired their homes. The birds a____made their homes safer.

    Many birds brought twigs (细枝) and leaves and others wove(编织) their nests."We  s____also store some food for our children," said one of the birds. And they collected food until they had enough to see them through the rainy season. They kept  t____busy getting ready for the bad times.

    Soon the rain came. It was f____by thunder and lightning. All the animals and birds stayed at their homes. It kept raining for many days. One day, a monkey wet in the rain came into the jungle. He sat on a branch(树枝), shaking w____cold.

    The poor monkey tried his best to get a place, but f____. The leaves were not enough to save him from the rain."Brrr! Itis so cold!" said the monkey. The birds were watching all this. They felt sorry for the monkey,  b____there was little they could do for him. One of them said. "Brother! Our small nests are not big enough to give you shelter." Another bird said, "All ofus prepared for the rainy season. If you had, you would not be in this difficult  s____".

    "How dare you tell me what to do?" said the monkey, shouting at the "bird. The monkey  a____hit the bird's nest and threw it on the ground. The bird and her babies were helpless.

    The poor birds thought, "Fool never value(重视) good advice. It is better not to advise them ".