如图，流出纸面的电流为2I，流进纸面的电流为I，则下述各式中哪一个是正确的？<img src="https://static.zxtiku.com/wangke/imgs/topic/51387eb0de743205b1ff4e859cfc9466.jpg"/><br/> A、<img src="https://static.zxtiku.com/wangke/imgs/topic/da07179511c645e0e6f54c1304007246.jpg"/><br/> B、<img src="https://static.zxtiku.com/wangke/imgs/topic/83fdc31b488929a0752815120aedfeeb.jpg"/><br/> C、<img src="https://static.zxtiku.com/wangke/imgs/topic/abbeef1765fe185ca97f576e7e60862f.jpg"/><br/> D、<img src="https://static.zxtiku.com/wangke/imgs/topic/20728cd99d682678df4b0cd9523bebb2.jpg"/>