I am sorry about dragging this question out.
1) I have lived in the USA for two years.
2) I had lived in the USA for two years.
3) I lived in the USA last year.
I know what difference there is between #1 and #2 and I think present and past perfect tense go well with for because actions in the tenses persist for a while, but past verbs go well with last year because actions in the past tense finish at a point. However, we can see past verbs with for, for example, 4) I lived in the USA for two years and I think #2 and #4 are acceptable and have the same meaning. What do you teachers think about it?
P.S I know that had p.p has two possible meanings: one is a past form of have p.p, and the other is the more past than the past.
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