Bunuel
In a seminar paper delivered at the annual American Psychological Association conference, Dr. Spagnoli distinguished pronounced alterations in mood, which may be frequent and occasionally severe without their constituting a clinical illness, from bipolar disorders.
(A) pronounced alterations in mood, which may be frequent and occasionally severe without their constituting a clinical illness, from bipolar disorders
(B) bipolar disorders and pronounced alterations in mood, occurring frequently and occasionally severely, without constituting a clinical illness
(C) pronounced alterations in mood, perhaps frequent and occasionally severe without constituting a clinical illness, and bipolar disorders
(D) between pronounced alterations in mood, which may be frequent and occasionally severe without constituting a clinical illness, from bipolar disorders
(E) between pronounced alterations in mood, which may be frequent and occasionally severe without constituting a clinical illness, and bipolar disorders
KAPLAN OFFICIAL EXPLANATION:
Before moving to the question of expression, start with grammar. The answer choices provide you with some different idioms so let's start there. The verb distinguished needs to be followed by from unless it's followed by between, so eliminate (B) and (C). Between appears in (D) and (E) and, as you know from earlier examples, between must always be followed by and. Eliminate (D) for pairing between and from. Finally on the question of expression, (E) is superior to (A) because (A) contains an unnecessary their. (E) is the winner.