表示时间的介词：
( 1) in, on， at在……时
in表较长时间，世纪朝代时代、年、季节、月及一般(非特指)的早、中、晚
如： in the 20 th century, in the 1950 s, in 1989, in summer, in January,
in the morning, in the night, in one's life, in one's thirties
on表示具体某一天及某一天的早、中、晚。
如： on May 1 st, on Monday, on New Year's Day, on a cold night.
in January, on a fine morning, on Sunday afternoon.
at表示某一时刻或较短暂的时间，或泛指圣诞节，复活节等。
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
" in+段时间"表示将来的一段时间以后;
" after+段时间"表示过去的一段时间以后;
" after+将来点时间"表示将来的某一时刻以后。
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……
from仅说明什么时候开始，不说明某动作或情况持续多久;
since表示某动作或情况持续至说话时刻，通常与完成时连用。
例句： He studied the piano from the age of three.
They have lived here since 1978.
( 4) after, behind在……之后
after主要用于表示时间;
behind主要用于表示位置。
例句： We shall leave after lunch.
Lucy is hiding behind an old house.
