熔断器保护的选择性要求是() ["后级短路时前、后级熔丝应同时熔断","前级先熔断,后级起后备作用","后级先熔断,以缩小停电范围","后级先熔断,前级1min后熔断"]
瘾疹的发生与以下因素有关,除了:() ["物理因素","他人传染","精神因素","感染因素","遗传因素"]
交流耐压试验加至试验标准电压后的持续时间,凡无特殊说明者为() ["30s","45s","60s","90s"]
独立避雷器(线)的接地网与电气设备接地网的距离不应小于() ["1m","2m","3m","5m"]
一个患黄癣的患儿,在其头部可见以下皮损,除了:() ["萎缩性瘢痕","碟形污黄厚痂","鼠尿臭味","毛发距头皮2~5mm处折断","发变枯黄弯曲,易拔出但无折断"]
森林病虫害防治实行()的方针。