Over the next few years, increasing demands on the Chattahoochee River, which flows into the Apalachicola River, could alter the saline content of Apalachicola Bay, which would rob the oysters there of their flavor, and to make them decrease in size, less distinctive, and less in demand.

A. which would rob the oysters there of their flavor, and to make them decrease in size

B. and it would rob the oysters there of their flavor, make them smaller

C. and rob the oysters there of their flavor, making them decrease in size

D. robbing the oysters there of their flavor and making them smaller

E. robbing the oysters there of their flavor, and making them decrease in size

I selected C as rob seems parallel with alter. But OA is D. Apart from the logic that robbing is dependent on alteration of saline content, is there any other reason why C is incorrect ?