用一个动滑轮将400N的货物提高lm，所用的力是250N，则力所做的功是____J，有用功是____J，机械效率是____。
500，400，80%
Why is he always forcing his daughter to practice playing the piano if she is not __________ a pianist?
A．meant
B．intended
C．trained
D．asked
员工更希望有个什么样的管理者：（）
A.像朋友一样
B.受他尊敬
C.像专家一样
D.有威慑力
