镗床进行镗削加工时,被加工工件表面产生波纹的原因是()。
A.电动机振动
B.机床振动
C.刀具振动
D.刀具振动
E.工件振动
F.刀杆振动
参考答案:A, B
The TV set he _____ works well now. [ ]
A. has repairing
B. having repaired
C. has been repaired
D. has had repaired
缺血性心脏病最常见的病因是()
A.主动脉狭窄
B.心肌肥厚
C.严重贫血
D.冠状动脉粥样硬化
E.主动脉瓣关闭不全