__________ she couldn't understand was__________ fewer and fewer students showed interest

in her lessons.

A．What; why

B．That ; what

C．What ; because

D．What;which

如图所示，原来静止的圆形线圈通以逆时针方向的电流I，在其直径AB上靠近B点放置一根垂直于线圈平面的固定不动的长直导线，并通以电流I′，方向如图．线圈上A点处受到的安培力力大小为______；而圆形线圈将______动．