David, Moderator posted:I agree with Gustavo's explanation and would simply like to add that because "for" is used (rather than "in") "have written" is impossible. The sentence "I have written two letters for three hours" makes no sense whatsoever.
Definitely, David. I just realized that, rather than saying that in Egyptian2017's sentence "have written" could be used with another adverbial, I should have said that "have written" could only be used with another adverbial, or should be used with another adverbial, which is what I meant to say. Thank you for noticing the ambiguity and making that clear.