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 hasnt 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?
---Hes already been sent for.
Tom has written a letter to his parents last night.
Tom wrote a letter to his parents last night.