First we need to ask some questions:
HAS SEEN or SAW?
Has the time period finished?
If the time period has NOT finished, we use the present perfect tense.
➨I have seen my old friends this month. (This month has not finished yet.)
The simple past tense is used when the time period HAS finished.
➨I saw my old friends last month. (Last month has finished.)
HAS CRASHED or CRASHED?
Is it new information or old?
We usually use the present perfect tense when we giving recent news.
➨Marry has crashed her car again. (This is new information.)
When giving older information, we use the simple past tense.
➨Marry crashed her car last year. (This is old information.)
I HAVE DONE or I DID?
Is it a specific time?
The present perfect is used when the action was done at some non-specific past time(s).
➨I have done this before. (We don’t know when.)
The simple past is used the action was done at a specific past time.
➨I did that last week. (We know exactly when.)
HAVE LIVED or LIVED?
Has the action finished (sentences with “for” or “since”)?
The present perfect is used with “for” and “since” when the actions have NOT finished yet.
➨We have lived in France for 10 years. (We still live in France.)
The simple past is used with for when the actions have already finished.
➨We lived in France for 10 years. (We don’t live in France now.)