求助一道语法题的正确答案，为什么有不同的版本

亲爱的敌人

In large doses, analgesics that work in the brain as antagonists to certain chemicals have caused psychological disturbances in patients, which may limit their potential to relieve severe pain.

(A) which may limit their potential to relieve
(B) which may limit their potential for relieving
(C) which may limit such analgesics’ potential to relieve
(D) an effect that may limit their potential to relieve
(E) an effect that may limit the potential of such analgesics for relieving



这道题的答案到底是D还是E，楼主选的E，看了网上一些论讨里有人说选E，可楼主的资料书里正确答案是D。


在做这道题的时候楼主在D和E之间也纠结了很久，因为D中their指代不明，前面出现了很多复数名词，E又不如D简洁


所以这题到底选什么

亲爱的敌人

开始写错了，楼主的资料书里选D

emmahiggins09

同意楼上的，我也觉得应该是E ，D里面的their 指代不清楚

nmamazon

Ｄ里their指什么/谁？analgesics？certain chemicals？psychological disturbances？还是patients？
E 直接提到 analgesics