Why Is the Yield to Maturity of a Zero-Coupon, Risk-Free

Why is the yield to maturity of a zero-coupon, risk-free bond that matures at the end of a given period the risk-free interest rate for that period?

A) Since a bond's price will converge on its face value as the bond approaches the maturity date, the Law of One Price dictates that the risk-free interest rate will reflect this convergence.
B) Since such a bond provides a risk-free return over that period, the Law of One Price guarantees the risk-free interest rate be equal to this yield.
C) Since interest rates will rise and fall in response to the movement in bond prices.
D) Since there is, by definition, no risk in investing in such bonds, the return from such bonds is the best that can be expected from any investment over the period.