压缩机油粘度变化在（）以上，就应换新油。 A.5%～10% B.10%～15% C.

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问题单项选择题

压缩机油粘度变化在（）以上，就应换新油。

A.5%～10%

B.10%～15%

C.15%～20%

D.20%～25%

答案

参考答案：B

单项选择题

Questions 1-4

What is typical of "umbrella species"？（）

A．Their survival is closely related to numerous other species living in the same habitats.

B．Their enormous size makes them the king animals superior over numerous other species.

C．They usually live on top of the mountains so that it is difficult for humans to hunt.

D．They enjoy privileges as with special measures and extra protection from human beings.

单项选择题

（2008）一定量的理想气体在进行卡诺循环时，高温热源温度为500K，低温热源温度为400k，则该循环的效率为：（）

A.56%

B.34%

C.80%

D.20%