高速钢淬火后的正常组织是隐针马氏体+碳化物+较大量残余奥氏体。（）
参考答案：对
Although a sudden change can be a bad thing, it might often be _____ in the long run.
A．beneficial
B．especial
C．disturbing
D．available
叙述离心泵的工作原理？
