Maria, do you have to go to bed ____ 10: 00 every night? [ ]
A. of
B. in
C. on
D. by
答案:D
哪种材料为封闭剂的主要成分
A.树脂基质
B.稀释剂
C.引发剂
D.辅助剂
E.以上均不是
水轮发电机定子主要由哪些部件组成?