gwd1-q30，关于后置用逗号隔开的分词是否有歧义的问题

The ancient Anasazi harvested such native desert vegetation as the purple-flowered bee plant, what they now commonly call wild spinach in northern Arizona and other parts of the southwestern United States.

A.      what they now commonly call

B.      a plant that they now commonly call

C.      now commonly called

D.      and is mow commonly called

E.       which it is now commonly called

答案是C，是省略了which is的结构，构成了-ed分词，修饰the purple-flowered bee plant。

但是为什么这里的-ed分词结构怎么这么确定没有歧义呢？

我在做题过程中发现，似乎在GMAT中，-ing分词不推荐用“逗号+-ing分词”后置的结构，修饰紧邻其前的名词，即***n.，-ing分词...，因为这样会有歧义，让人不清楚是修饰主句主语，还是临近名词的。但是这种结构在其紧邻名词位于一个主句的介词短语中，即***in/ with/ on ***n.，-ing分词...，貌似就可以，例子我一下找不到了，但是好像有这么个印象，不知道是不是这样呢？如果是这样，是否-ed分词也符合这个规律？请NN们指点~

顶~这题的-ed分词用逗号隔开后置，修饰其临近的非主语名词，为什么没有歧义呢？为什么 now commonly called 不会被认为是修饰主句主语The ancient Anasazi
                    的呢？请NN们关注一下~帮我解答解答~谢谢啦~

醍醐灌顶啊~非常感谢AlicenX,你这么说我就明白了~