I had too much work to do last night. I didn't go to bed ___________ 11 o'clock.
A:at
B:until
C:for
D:In
a、b、c三盏灯分别标有“110V 20W”、“220V 40W”、“36V 60W”的字样,三盏灯都正常发光,比较它们的亮度( )