A note of the Present Perfect
have/has verb +ed OR past participle
Regular verbs: verb+ed Irregular verbs: past participle (p.129)
Time expressions: already, just and yet
examples:
He has worked there. I have eaten all of my lunch. -> Positive
He has not worked there. I have not eaten all of my lunch. -> Negative
Has he worked there? Have I eaten all of my lunch? -> Question
PAST SIMPLE AND PAST PARTICIPLES ARE DIFFERENT, DON'T MIX THEM!!!