下列哪些仪器工作时主要应用了电磁感应原理A.日光灯 B.示波管 C.变压器 D.质谱仪 答案:AC 示波管的原理是带电粒子在电场中的偏转,质谱仪主要是带电粒子在磁场中做圆周运动,故A、C正确,B、D错。6.一Where is Jason?I want to tell him about the result of the singing competition.一Oh,you .He has known it already.( )A.can'tB.mustn'tC.needn'tD.shouldn't