现在完成时have done 的时间标志是
in the past few/three years
since + 时间点/ sb dis
副词标志是
already,yet,never,ever
现在完成时可以单独使用
i have finished homework.
但过去完成时不可以单独使用
用在“It is the first/second...time+that”从句中
过去完成时 had done
时间标志
by last year/by the time of
过去完成时一般和过去时一起出现
sb had done sth before sb did
sb did sth after sb had done
用于hardly when,no sooner than的句式中
we had hardly came home when it rained.
用在“It was the first/second...time+that”句型中