[问答题] 重大电网事故如何调查？

一级风险是现金出纳柜台（）以上的营业场所。 ["6个（含6个）","8个（含8个）","7个（含7个）","5个（含5个）"] Structural bulkheads on a ship are usually（）. ["continuous","watertight","transverse","non-watertight"] 为了敷设方便，截面积大于（）的电缆采用单芯电缆，截面积大于（）的电缆则采用两根较小截面积电缆并联的方式来代替。 ["15mm^{2<\/sup>；80mm2<\/sup>","25mm2<\/sup>；120mm2<\/sup>","25mm2<\/sup>；75mm2<\/sup>","15mm2<\/sup>；100mm2<\/sup>"] 电视监控的存储时限不应少于（）。 ["5个月","30日","3个月","2个月"] Signs of racking stresses generally appear at the（）. ["bow and stern shell frames and plating","junction of the frames with the beams and floors","garboard strake，at each side of the keel","thrust bearing of the main shaft"] 重大电网事故如何调查？}