prep CR 69 求解答！

DQStephanie

Southington University's fund-raisers succeeded in getting donations from 80 percent of the potential donors they contacted this year. This rate would be the expected rate if the only potential donors contacted were those who have donated in the past. But good fund-raisers constantly contact less likely prospects in an effort to expand the donor base. Thus the high success rate, far from showing that the fund-raisers did a good job, shows insufficient canvassing effort. Which of the following, if true, most seriously weakens the argument?
A. Among potential donors contacted by Southington University's fund-raisers, the majority of those who did not make donations were people who had made donations to the university in the past.
B. The amount of money raised by Southington University's fundraisers this year was lower than the amount they had raised in any of the previous several years.
C. Individual donations made to Southington University this year were, on average, slightly larger than were average individual donations made to many other universities.
D. Fund-raisers contacting past donors are not only to get new donations but also to get names of potential new donors to contact.
E. The majority of the donations that fund-raisers succeeded in getting for Southington University were from donors who had never given to the university before.

the correct answer is E.
I chose E, but I'm confused about chioce A.
A says that the majority of potential donors contacted by fund-raisers who did not make donations were people who had made donations in the past. I think this is an irrevelant option since the conclusion we want to weaken is "fund-raisers didn't try to expand the donor base." However, A just told us who didn't make donations but said nothing about who did make donations. If the majority of people who made donations are also people who made donations before, then the answer is actually strengthen the argument.
The above is my thoughts. Could anyone correct me if I got something wrong?
Thanks!