题目

Jack Smith earns ______his wife Jane while they do the same amount of work, which is unfair. A . twice as many as B . as twice much as C . twice more money as D . twice as much as 答案：D一矩形线圈位于一随时间t变化的匀强磁场内，磁场方向垂直线圈所在的平面（纸面）向里，如图（甲）所示。磁感应强度B随t的变化规律如图（乙）所示。以I表示线圈中的感应电流，以图（甲）中线圈上箭头所示方向的电流为正，则以下的图中正确的是（   ）