The "may" that you mentioned already softens "will." So this may be a sign that prices will stay higher. Then again, it may not be such a sign, in which case prices may not stay higher.
As for "they" in D, I don't see a problem there. Prices are going to stay higher than prices usually do. We don't need the word "prices"--or even the word "they"--but the meaning is clear enough.
As for "they" in D, I don't see a problem there. Prices are going to stay higher than prices usually do. We don't need the word "prices"--or even the word "they"--but the meaning is clear enough.
