电气火灾的原因主要有（）、（）、（）和（）四种。
参考答案：短路；过负荷；接触电阻电火花；电弧
That rude boy ________ have rushed out of the classroom when Ms Green was giving a lecture, which
finally led to his being punished by the head teacher.[ ]
A．could
B．must
C．dare
D．should
简述低电压穿越（LVRT）。具体我国电网公司是如何规定的？
