prep 12的一道逻辑题，搞不懂里面的逻辑链，求指教

哎唷不小心

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.
可以解释下整道题的逻辑链么，好晕啊，不知道这题主要在讲些什么
谢谢~