--Hey, Tony, You look so tired today.

---I __ until 12 o' clock last night for the math test.

A. woke up                 B. stayed up                C. grew up

一盏电灯接在恒定电压的电源上，其功率为100W。若将这盏电灯先接在一段很长的导线后，再接在同一电源上，以知导线上损失功率是9W，则此时电灯实际消耗功率是 [ ]

A.91W

B.小于91W

C.大于91W

D.条件不足，无法确定