如图所示电路中,已知R1>R2,电源电压U保持不变,在相同的时间内四个电路中总共放出的热量由多到少的顺序是
A:甲、乙、丙、丁
B:甲、丙、丁、乙
C:丙、丁、乙、甲
D:乙、丁、丙、甲
Paper ______ invented by Chinese many years ago.