题干
Do you have any idea______ is actually going on in the classroom?
A：that
B：what
C：a
D：which
答案(点此获取答案解析）
B
A：that
B：what
C：a
D：which
。流经导线的电流为I，方向如图中箭头所示。导线段abcd所受到的磁场的作用力的合力
