What Is Meant by the Real Risk-Free Rate of Interest

What is meant by the real risk-free rate of interest?

A) The opportunity cost of foregoing consumption,representing the rate that must be offered to individuals to persuade them to save rather than consume.
B) The rate actually used in the market,not in textbooks.
C) The rate quoted on short-term Treasury bills.
D) The nominal risk-free interest rate,less the expected inflation.