问题描述：
(),we must do work on the machine.A for a machine to do work B for a machine doing work C for ...
(),we must do work on the machine.
A for a machine to do work B for a machine doing work C for a machine is doing work D a machine works 为什么选A啊?
(),we must do work on the machine.
A for a machine to do work B for a machine doing work C for a machine is doing work D a machine works 为什么选A啊?
问题解答：
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