A self-contained breathing apparatus is used to（）.

A.make underwater repairs to barges

B.determine if the air in a tank is safe for men

C.enter areas that may contain dangerous fumes or lack oxygen

D.resuscitate an unconscious person

我国66kV及以下电压等级的电网中，中性点采用中性点不接地方式或经消弧线圈接地方式。这种系统被称为小接地电流系统。（）