对叶片泵采用切削叶轮的方法，可以改变水泵性能曲线。
参考答案：对
（）用于尺寸小、载荷低、主要承受磨损的零件，如活塞销、小轴等。
A．20Cr
B．20CrMnTi
C．18Cr2Ni4WA
D．20
When the girl learnt that her boy friend was ____ in the earthquake, she _____.
A．injured; burst in tear
B．killing; burst into tears
C．still alive; burst into tears
D．missing; burst into laughter
