I have a history class at 9 o'clock.

　　我9點鐘有歷史課。

　　We arrived at two o'clock and left at ten past.

　　我們兩點鐘到達，十分鐘后離開。

　　I have to collect the children from school at 3 o'clock.

　　我得在3點鐘到學校接孩子。

　　By my watch it is two o'clock.

　　我的表是兩點鐘。

　　At the first stroke it will be 9 o'clock exactly.

　　等到鐘敲第一下時就是9點整。