The source of this question is SC1000. According to the answer guide, the correct answer is E. I chose D, assuming that it was more idiomatic (and concise). What is the correct idiom? “Potential to” or “potential for”?

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

I am not sure about the right idiom. But D cannot be the right answer. 'their' in D seems to be ambiguous in that it doesn't seem to refer to anything specific. E resolves that issue by saying 'limit the potential of such analgesics'

Every answer choice is problematic; don't study this problem
:)