(1)in , on，at 在……时
如：in the 20th century, in the 1950s, in 1989, in summer, in January,
in the morning, in the night, in one's life , in one's thirties
如：on May 1st, on Monday, on New Year's Day, on a cold night .
in January, on a fine morning, on Sunday afternoon.
如: at 3:20, at this time of year, at the beginning of, at the end of …,
at the age of …, at Christmas， at night, at noon, at this moment
在last, next, this, that, some, every 等词之前一律不用介词
如：We meet every day.
(2)in, after 在……之后
例句：My mother will come back in three or four days.
He arrived after five months.
She will appear after five o'clock this afternoon.
(3)from, since 自从……
例句：He studied the piano from the age of three.
They have lived here since 1978.
(4)after, behind 在……之后
例句：We shall leave after lunch.
Lucy is hiding behind an old house.