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
Tony loves exciting things. He trekked the forests by himself last summer.
中学阶段是人生最宝贵的时期。要珍惜,要拼搏,享受成长。这启示我们进入中学,要( )
物体以一定的初速度从斜面底端A点冲上固定的光滑斜面,斜面总长度为l,到达斜面最高点C时速度恰好为零,如图,已知物体运动到距斜面底端处的B点时,所用时间为t,则物体从B滑到C所用的时间为____.