发电机冷却效果最好的是()。
A、空气冷却;
B、氢气冷却;
C、水冷却
参考答案:C
Famous as he was, he was reluctant to be the _____ of public attention. [ ]
A. focus
B. middle
C. key
D. point
交流电磁铁在吸合过程中,工作电流的大小是()。