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）
(E) an effect that may limit the potential of such analgesics for relieving
请问代词在句子中的指代顺序，我以为their在句子中首先是指代主语，也就是analgesics，所以选了D，不知道错在哪里？
