【单选题】All naturally occurring forest fires are caused by lightning strikes.
【单选题】Weather forecasts___more hot weather, gusty winds and lightning strikes.
【简答题】A.Criminals who set the fires on purpose. B.Natural lightning strikes. C.Sparks from vehicles. D.Carelessly discarded cigarettes.
【简答题】( )失去整体稳定时,该结构件应判为不合格。 A.重要结构件 B.一般结构件 C.结构件 D.齿轮表面
【简答题】什么叫正接法、反接法?如何选择直流电源的极性?