In the field of finance, the return on U.S. T-Bills is assumed to be the best estimate of a risk-free rate that we have. The return on short-term (less than one year) T-Bills is assumed to be composed of

a. the real risk-free rate and a maturity risk premium.

b. the real risk-free rate and a premium for inflation.

c. a default risk premium and a maturity risk premium.

d. a default risk premium and a liquidity premium.