（1）表示“某一具体时刻（即几点几分时）”,须用介词at.例如：
He gets up at six o''''clock every day .他每天六点起床.
I got home at five thirty yesterday afternoon.我昨天下午五点半到家.
（2）用在特定的时候（时节、时机）时,须用介词at.例如：
They were happy at that time.他们那时很幸福.
I think the shop is clcsed at this time lf
day.我认为商店在白天的这个时候关门了.
（3）表示“在中午、在夜晚、在周末”时,须用介词at.例如：
What do you often do at noon?你中午经常做些什么?
You can see many stars in the sky at night.夜晚你能看到天空中有许多星星.
（4）表示“在……岁”时,须用介词at.例如：
At the age of nine ,the boy could swim
well.在九岁的时候,这孩子就游泳游得很好了.
At the age of twenty,I began to teach English at this
school.在二十岁的时候,我就开始在这所学校教英语了.
