井下电气设备必须符合防爆要求,应有()、()和()保护装置。
参考答案:接地、过流、漏电
The boy the first prize, but he was so careless as to make a foolish mistake.
A.must have gained
B.need have gained
C.could have gained
D.shall have gained
系统容量和大机组经济容量保持怎样的比例较为合适?