"A. rethoric" is the best option to complete the sentence because it is clearly the meaning for "effective writing and speaking while artfully using persuasion". It means that to effectively write and speak, people should use persuasion artfully and creatively for their own purposes, rather than only focusing on grammar rules (which are important but not the final aim to be achieved). Letter B is only a redundancy, while letter C does not appy to the sentence because "manipulation" is totally different from persuasion, and letter D does not apply as well, because they sound more like argumentative, rather than persuasive features.
