A:85
B:255
C:341
D:1023
There is a sofa (沙发)in this room. We chat (聊天)with each other and watch TV in this room. It's a____.
如图所示,真空中M、N处分别放置两等量异种电荷,a、b、c表示电场中的3条等势线,d点和e点位于a等势线上,f点位于c等势线上,df平行于MN.以下说法正确的是( )