电阻R1、R2并联时，两电阻功率之比 P1 P2 = U2 R1 U2 R2 = R2 R1 = 4 3 ；电阻R1、R2串联时，两电阻功率之比 P′1 P′2 = I2R1 I2R2 = R1 R2 = 3 4 ．故选B．
