He has nothing to say, ?[ ]
A. has he
B. hasn't he
C. does he
D. doesn't he
答案:C
隔爆型电气设备的防爆关键在于()。
A、内部结构
B、外部结构
C、隔爆电路
D、隔爆外壳
造成女性不孕的最常见原因是
A.不排卵B.输卵管因素C.重度宫颈糜烂D.子宫内膜异位症E.子宫黏膜下肌瘤