汽供给水泵汽轮机叶轮上均设有（），供动平衡用。
参考答案：动平衡槽
—I regretted what I have done.
—_______ gone is gone. ______ no use regretting it any more.[ ]
A. What's; That's
B. It's; That's
C. What's; It's
D. That's It's
某项目的净现金流量如下，试计算其投资回收期( )。
A．年份
B．0
C．1
D．2
E．3
F．4
G．净现金流量
H．-100
I．50
J．40
K．50
L．70
