Which of the following firms would be expected to have a high ROE based on that firm's high operating efficiency? Select one O a. a grocery store chain that has very high turnover, selling many multiples of its assets per year Ob a brokerage firm that has high levels of leverage Oc a high-end fashion retailer that has a very high mark-up on all items it sells O d. a medical supply company that provides very precise instruments at a high price to large medical establishments such as hospitals