GMAT Sentence Correction (SC) | Contemporary film directors, some of them write the scripts for, act i

First: Option a is wrong because the part "some ofthem write the scripts for, act in, and even produce own motion pictures" is an indepedent clause separated only by a comma without any conjunction. An indepedent clause cannot act as a subgroup modifier. In option d, "some ofwhom write the scripts for, act in, and even produce " is a dependent clause, and can act as a subgroup
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