关于电磁感应现象中,通过线圈的磁通量与感应电动势关系正确的是 A.穿过线圈的磁通量越大,感应电动势越大 B.穿过线圈的磁通量为零,感应电动势一定为零 C.穿过线圈的磁通量变化越大,感应电动势越大 D.穿过线圈的磁通量变化越快,感应电动势越大 答案:D20.---I got up at five this morning, I thought it was Friday. ---You _____ so early.It is Sunday today; you don’t have to go to work.A.mustn’t have got up B.needn’t have got upC.needn’t get up D.mustn’t get up