(British English and American English have different rules for the use of the present perfect. The comments being made here and the exercises state the correct grammar for British English. However, in American English, it is often considered acceptable to use the past simple in some of these examples.)
We use the present perfect when we want to look back from the present to the past.
We can use it to look back on the recent past.
Often when we look back on the recent past we use the words 'just' 'already' or the word 'yet' (in negatives and questions only).
We can also use it to look back on the more distant past.
Often when we look back on the more distant past we use the words 'ever' (in questions) and 'never'.
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