I have a history class at 9 o'clock.
我9点钟有历史课。
We arrived at two o'clock and left at ten past.
我们两点钟到达，十分钟后离开。
I have to collect the children from school at 3 o'clock.
我得在3点钟到学校接孩子。
By my watch it is two o'clock.
我的表是两点钟。
At the first stroke it will be 9 o'clock exactly.
等到钟敲第一下时就是9点整。