当负荷工作在（）情况下，热继电器正常工作，长期不动作。 ["6倍额定电流","1倍额定电流","1.2倍额定电流","1.5倍额定电流"]
北部非洲有哪些主要特点？
Combustible gas indicators operate by drawing an air sample into the instrument（）. ["over an electrically heated platinum filament","where it is mixed with nitrogen","where it is ignited by a sparking device","where its specific gravity is measured"]
与苏宁和国美相比，京东商城的成本较低的原因是（）。 ["政府扶持","进货渠道宽","广告费用低","通过技术"]
非洲的粮食问题长期得不到解决的主要原因何在？
亚共析钢的淬火加热温度是什么？加热温度过高或过低会产生哪些问题？
