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.
句子中如有过去时的时间副词（如 yesterday, last, week, in 1960）时，不能使用现在完成时，要用过去时。
（错）Tom has written a letter to his parents last night.
（对）Tom wrote a letter to his parents last night.