(2 points) According to what we have learned in this class, what is the key distinction between the short-run and the long-run? O All costs are variable in the short-run while some are fixed in the long-run O All costs are variable in the long-run while some are fixed in the short-run O Sunk costs should affect our decision in the short-run but not in the long-run O It may be optimal to accept negative profit in the long-run, but not in the short-run