I would say the answer would be A) choice of words.
An essay is based upon words. The way you use them and the way someone else reads them.
for example, lets say its a persuasive essay. If you dont use the right words to explain why you think your side is right or better, the reader will read and think what you have wrote either doesnt make sense or misunderstand what you are trying to say.
I hope this helped! :)
