题目

Have you ever considered why you begin yawning too when you see someone yawn? Or how hard it is to be among people laughing and not laugh yourself? Well, apparently it's because we have mirror neurons (神经元）in our brains. Put simply, the existence of mirror neurons suggests that every time we see someone else do something, our brains imitate it whether or not we actually perform the same action. This explains a great deal about how, we learn to smile, talk, walk, dance or play sports. But the idea goes further: mirror neurons not only appear to explain physical actions, they als在图所示的电路中，电源电压保持不变，当开关S1、S2都闭合时，电压表V1、V2的示数之比为5∶3；当开关S1闭合、S2断开时，电压表V1、V2的示数之比为3∶2．在后一种情况下的全部通电时间内，电阻R1与R3产生的热量之比为 [　　] A．2∶3B．1∶3 C．3∶2D．2∶1