Value of marginal product (VMP) differs from marginal revenue product (MRP) in that:
a.        MRP measures the value society places on the next worker’s output while VMP measures the value the firm places on the next worker’s output
b.*        VMP measures the value society places on the next worker’s output while MRP measures the value the firm places on the next worker’s output
c.        MRP always exceeds VMP
d.        VMP always exceeds MRP

为什么选B呢？