The logic here is:
Since the textbook recieved the highest ratings -> The books were chosen becasue of their acedemic value and not because of the donation.
We are looking to weaken that connection.
(A) Does that. It gives us a reason why the committee chosing the books is connected to the donation.
(B) Does not address the gap.
(C) Could be temping. But is out of scope. It does not weaken the connection between the award and why the book was chosen. What they used last year has no bearing on the issue.
(D) trying to mislead you by mixing info. There is no reason to think the donation would effect her more if she was on the committee.
(E) Also temping, but still does not indicate the donation was a factor in the committees choice.