机组振动有哪几方面的原因？
参考答案：
（1）机械原因；（2）水力原因；（3）电气原因。
—Hello, this is Lily speaking.Could I speak to Mr. Black?
—…Sorry. He ______ the Xuanwu Lake Park. [ ]
A. has been to
B. went to
C. has gone to
D. will go to
弗洛伊德认为，道德性焦虑中的危险来自于（）。
A.超我
B.冲动
C.自我
D.现实
