用H2置换发电机内CO2的操作。

小卖部有一种计算器，原价是72元，八折后的价钱是多少？

Many people who had seen the film were afraid to go to the forest when they remembered the scenes__________people were eaten by the tiger.

A．in which

B．by which

C．which

D．that

梁在约束扭转时，截面上产生剪应力有（）和弯曲扭转剪应力两种。

如果NPV＞0，这种股票价格被高估，因此不可购买这种股票。( )

列选项中，不属于液压支架的承载结构件的是（）。

A、顶粱

B、掩护梁

C、四连杆机构

D、千斤顶