What, Typically, Is Used to Calculate the Opportunity Cost of Capital

Multiple Choice

What, typically, is used to calculate the opportunity cost of capital on a risk-free investment?

A) the best expected return offered in any investment available in the market
B) the interest rate on U.S. Treasury securities with the same term
C) the interest rate of any investments alternatives that are available
D) the best rate of return offered by U.S. Treasury securities