The "market risk premium" is most closely measured as

a. the difference between the return on a small firm mutual fund and the return on large index such as the Standard and Poor's 500 index

b. the return on a large index fund (such as the S&P 500)

c. the difference between the return on a large index fund (such as the S&P 500) and the return on Treasury bills

d. the difference between the return on the risky asset with the lowest returns and the return on Treasury bills

e. the difference between the return on the highest yielding asset and the lowest yielding asset