Answer: C. "You do a good job of establishing your central claim early in the essay; be sure to back it up with supporting evidence."
Explanation: the big picture is something that represents the entire perspective on a situation or issue, in this case, a "big-picture feedback" is an opinion or advice that doesn't focus in the specific details, but instead, focus in the general word. From the given options, the statement that is an example of big-picture feedback is the corresponding to option C, because it is giving advice about the written work in general (the other options focus on details like the typos, paragraphs or sentences).