GMAT Sentence Correction (SC) | Re: Bluegrass musician Bill Monroe, whose repertory, views on

HIbrightandamen ,

so in C & D usage of firstWAS iswrong:

Monroe
whose views WAS influential
was also an inspiration
the subject "views" is plural, so you need WERE not was.

INFLUENCED (Verb) is also better than WERE INFLUENTIAL (Adjective): VAN rule says preference order of verb, adjective and noun is:
Verb --> Adjective --> Noun

Hence B is correct.