— What were you doing at this time yesterday?
— I _______.
A:slept
B:am sleeping
C:was sleeping
D:sleeping
下列各句中,没有语病的—句是( )
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( )