请教版主和NN：og10-SC-15与og10-SC-18有一个语法点的疑问

          最近在总结OG10－SC－15的过程中，突然发现OG提供解释说，B，D中划黄色部分答案不正确（形容词短语修饰它之前的名词），应该改用C中划黄线部分的（定语从句修饰），但OG10—SC－18中黄色划线部题干就这样用的（形容词短语修饰它之前的名词），这就是说：其实这种表述方式是可以接受的，它们的差别在哪里？

         难道它潜台词的意思是说：在15题中，如果用形容词短评，就会有三个短语并列歧义的嫌疑？所以用定从来表示改正这个缺陷？也就是说，在这种情况下，GMAT更倾向于用句子来表示显示它没有歧义？还就是说，根本就不能用呢？这样的话，为什么18题又用了呢？我的理解有误吗？请指教！！

      先谢了

15. In his research paper, Dr. Frosh, medical 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.

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

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

(C)  between mood swings, which may be violent  without being grounded in mental disease, and
    genuine manic-depressive psychosis

(D)  between mood swings, perhaps violent without being grounded in mental disease, from
    genuine manic-depressive psychosis

(E)  genuine manic-depressive psychosis and mood swings, which may be violent without being
    grounded in mental disease

The best choice is C because it uses the idiomatically correct expression distinguishes between x and y and because it provides a structure in which the relative clause beginning which may be violent clearly modifies mood swings. The other choices use distinguishes in unidiomatic constructions. Additionally, their in A is intrusive and unnecessary, and the modifier of mood swings in B and D (perhaps violent) is awkward and less clear than the more developed clause which may be violent[CW1] .

当形容词被逗号隔开单独出现时，修饰的是整个句子。

15题： 这里的形容词要修饰的前面的名词mood swings，直接用形容词修饰就有歧义。加上 which 变成从句明确他的修饰对象。

18题：   这里的形容词修饰的是整个句子，不存在歧义问题。

Open to discuss...............

谢谢killer!!明白了