题干
After the UN Security Council imposed most serious sanctions on Pyongyang, is needed now is for all parties to show wisdom and patience.
A：which
B：what
C：that
D：who
答案(点此获取答案解析）
B
一个电阻，磁感强度垂直于导轨平面，金属棒和导轨的电阻不计，设MN下落过程中，电阻R上消耗的最大功率为P，要使R消耗的电功率增大到4P，可采取的方法是（ ）
