交流绝缘监视装置用于中性点非直接接地系统，利用零序电压可有选择性的监视哪条线路发生了接地故障。
查看答案
工厂供电系统中一般采用的是二次重合闸技术，即断路器被继电保护装置控制跳闸后，尝试重合两次恢复供电。
A. 对
B. 错
It is almost 3 years ___we saw each other last time.
A. before
B. since
C. after
D. when
__ you call me to say you're not coming, I’ll see you at the office.
A. Though
B. Whether
C. Unitil
D. Unless
They had camped once before,____ they knew what to take.
A. becuase
B. now
C. so
D. since
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