Sentence Correction

In his research paper, Dr. Frosh, director of the Payne Whitney Clinic, distinguishes mood swings, which may be violent without their being grounded in mental disease, from genuine manic-depressive psychosis

mood swings, which may be violent without their being grounded in mental disease, from genuine manic-depressive psychosis

mood swings, perhaps violent without being grounded in mental disease, and genuine manic-depressive psychosis

between mood swings, which may be violent without being grounded in mental disease, and genuine maniac-depressive psychosis

between mood swings, perhaps violent without being grounded in mental disease, from genuine maniac-depressive psychosis

genuine maniac-depressive psychosis and mood swings, which may be violent without being grounded in mental disease


Here I rejected A only because of its use of possessive pronoun 'their'.
However, the answer explanation says A fails to use the correct idiomatic expression, i.e. between x and y. My question:
Isn't the idiom distinguish x from y equally acceptable in A if 'their' is ignored?