yesterday, last week， ago, in1980, in October, just now, 具体的时间状语
this morning, tonight,this April, now, once，before, already, recently，lately
for, since, so far, ever, never, just, yet, till / until, up to now, in past years, always,
3)现在完成时可表示持续到现在的动作或状态，动词一般是延续性的，如live, teach, learn, work, study, know.
过去时常用的非持续性动词有come, go, leave, start, die, finish, become, get married等。
I saw this film yesterday.
I have seen this film.
Why did you get up so early?
Who hasn t handed in his paper?
She has returned from Paris.
She returned yesterday.
He has been in the League for three years.
He has been a League member for three years.
He joined the League three years ago.
I have finished my homework now.
---Will somebody go and get Dr. White?
---He s already been sent for.
Tom has written a letter to his parents last night.
Tom wrote a letter to his parents last night.