水泥，熟石灰等粉尘不宜采用湿式除尘器，主要是因为（）.
A.水泥和熟石灰属于憎水性粉尘
B.润湿性较
C.吸水后易结垢
D.没有润湿
参考答案：C
—He couldn't have finished his homework last night, _________he?
—No. You see, he is busy doing it now.[ ]
A. has
B. could
C. must
D. did
讨论断电器的闭合角，甲认为断电器触点间隙越大闭合角越大，乙认为断电器触点间隙越小，闭合角越大，你认为（）
A.甲对
B.乙对
C.甲乙都对
D.甲乙都不对
