It's raining outside, you'd better take your umbrella.
A:but
B:for
C:or
D:so
将L1“220V 40W”和L2“220V 100W”两只灯泡分别串联和并联后,接入电压可调的电源上.灯泡串联时,____消耗的功率较大,电路消耗的最大功率为____ W;两只灯泡分别串联和并联时,电路消耗的最大功率之比为____(电压不允许超过额定值,灯丝电阻不随温度变化)