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When writing an essay, tense agreement is important.

Once I decide to maintain the essay with the present tense, I should stick to it, shouldn't I?

Q) My question is, what about this situation:

Are the two tenses acceptable?; either present or present perfect like one underlined below. (assuming that I have maintained the present tense in the essay.)

ex) As feedback on this activity, the teacher may provide available advice on students' performance focusing on how effectively they have delievered the messages.
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Aside from any specific example, why do you think that you should use only one tense in an essay?
Comments  
Ah.. you wonder why we have to use only one tense?

No, what I mean is once I decide to focus on the present tense it'd be better not to go too often here and there.. Of course, it will depend on situations..

Anyway, my point is we don't need to use only one tense in writing.

My question is using have + p.p, as shown in my example, is acceptable when I choose to use the present tense as the main tense in my essay.

Your already answer that. Thank you anyway^^