离心泵产生振动的原因有（）。
A、泵轴和驱动机不同心
B、轴承损坏
C、转子不平衡
D、地脚螺栓松动
参考答案：A, B, C, D
- -Could you tell me ?
--Sorry, I don't know .I was not at the meeting.
A．what does he say at the meeting
B．what did he say at the meeting
C．what he says at the meeting
D．what he said at the meeting
在PhotoshopCS4中，像素的形状只有可能是（）。
A.矩形
B.圆形
C.正方形
D.菱形
