Re: present perfect versus simple past
As a footnote:
The present perfect often expresses a connection or continuum between a past action (or state) and the present.
Thus these two sentences may describe the same event:
1. I have eaten 6 chipolatas.
2. I ate 6 chipolatas.
but in #1, the speaker chooses to express a connection between the event and the time of speaking, whereas in #2 he doesn't.
Hence the unidiomatic nature of a sentence such as:
3. ??? I have eaten 6 chipolates last night.
"I have eaten" maintains the past-present connection; but "last night" places the action firmly in the past and thereby creates an incongruity.
Not a professional ESL teacher.