题目内容

It’s easy to forget that the _ for this have been one of the __ struggles for/in human history.

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Today 7 in 10 people on earth can having _ in their homes

__ that _ water thrived

( )能很好地承受径向载荷与单向轴向载荷的综合作用。

A. 深沟球轴承
B. 角接触球轴承
C. 推力球轴承
D. 圆柱滚子轴承

与滑动轴承相比,滚动轴承的优点是( )。

A. 节约铜、锡等贵重金属
B. 润滑油消耗少
C. 轴承噪声较小
D. 可以同时承受轴向和径向载荷