问题
选择题
It will be some years before some foreign doctors change the impression they have ____Chinese medicine, _____, in their opinion, is nothing but raw herbs and not effective at all in treating diseases. [ ]
A. for; which
B. on; what
C. to; that
D. on; which
答案
答案：D
”型装置，总质量为m，置于导轨上。导体棒中通以大小恒为I的电流（由外接恒流源产生，图中未画出恒流源）。线框的边长为d（d<l），总电阻为R，下边与磁场区域上边界重合。将装置由静止释放，导体棒运动到磁场下边界时速度恰好减为0，导体棒在整个运动过程中始终与导轨垂直。重力加速度为g。求：