如图,电路a、b、c分别表示电流表或电压表,电表都是理想的,则下列各组电表示数中可能的是() (A) a = 1A , b = 2V , c = 0 . 5A ( B ) a = 2V , b = 0 . 5A , c = 1A ( C ) a = 0 . 5A , b = 1A , c = 2V ( D ) a = 2V , b = 1A , c = 0 . 5A