GMAT Sentence Correction (SC) | Re: New fall shows added to the television

McQueen , the simple answer is that "while" is not a parallel marker. It indicates a modifier that builds on the earlier action. The fall shows have increased 3 things, and they have done all this while decreasing something else. Using a parallel verb linked with "and" or "but" would work as well, but there's nothing wrong with the modifier form in C. (I'm assuming you meant C, not D.)
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