Answer: I would contend that the right answer is the C. The ghost's mysterious appearance heightens the horror that Scrooge feels about the results of his life choices.
Explanation: Just to elaborate a little bit on the answer, it can be added that the ghost's appearance is neither dramatic nor unassuming, so options A and B should be discarded. Likewise, his appearance is not powerful, either, so option E should also be discarded. The narrator relates how the ghost's "mysterious presence" filled Scrooge with a grave fear, and since this ghost was the last one in visiting him, and by then he had seen very upsetting scenes, it can be concluded that his visit intensified the horror that he had been already feeling about the results of his life choices — such as his stinginess.