Choice C is the best answer because “designing” maintains parallelism with “evaluating,” “assessing,” and “improving.”

Choice A is not the best answer because “they design” does not maintain parallelism with “evaluating,” “assessing,” and “improving.”

Choice B is not the best answer because “to design” does not maintain parallelism with “evaluating,” “assessing,” and “improving.”

Choice D is not the best answer because “design” does not maintain parallelism with “evaluating,” “assessing,” and “improving.”