Jill is the best eye surgeon in town, and she earns $350,000 a year. Sierra is an average eye surgeon in town, and she earns $100,000 a year. Jill's skills as a surgeon are a. more expensive because she receives a compensating differential. b. valued less by the market relative to Sierra's and that explains why her income is higher than Sierra's. c. valued more by the market relative to Sierra's and that explains why her income is higher than Sierra's. d. valued less by the market relative to Sierra's and that explains why her income is lower than Sierra's