下列说法中正确的是（） A．一定省力的机械有杠杆、定滑轮_爱下问搜题

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问题选择题

下列说法中正确的是（　　）

A．一定省力的机械有杠杆、定滑轮

B．一定省力的机械有定滑轮、滑轮组

C．一定省力的机械有杠杆、动滑轮

D．一定省力的机械有动滑轮、滑轮组

答案

答案：D

选择题

— The patient looks much better. ____ is it that has made him ____ he is today?

— Perhaps the special medicine and his family's patient care. [ ]

A. What; that

B. That; that

C. What; what

D. What; which

单项选择题

关于干式回火保险器的特点，下列说法错误的是（）。

A.体积小

B.重量轻

C.阻火性能差