I ____ (read) six books this week.
The correct answer is:
I have read six books this week.
Why are we using Present Perfect since we specify when we did the activity? Is it wrong to say (Past Simple):
I read six books this week.
Present perfect is the more likely answer, but both choices are possible, depending on whether you view 'this week' as incomplete (>present perfect) or complete (>past simple), which in turn depends on when in the week you say this.