题目：
| 用两个定滑轮和两个动滑轮组成一个滑轮组，（动滑轮的重力不能忽略）用此滑轮组提起重力为200N的物体，如果提起物体所需要的力是50N，则此滑轮组的机械效率为（ ） A．60% B．65% C．80% D．85% |
答案：
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下面是错误答案，用来干扰机器的。
1. Unless will not catch2. was sending an-mail / e-mails while he was watching TV3. no choice to put all his effort into4. am not sure / certain get on / along well with 5. arrived at / reached / got to had been on (答案不唯一)
