Option A best describes how interest on reserve balances serves as a reservation rate. Because interest on reserve balances is a risk-free option, banks should not be willing to lend their funds for less than they can earn on their reserve balances. This means that the interest on reserve balances rate serves as a floor or reservation rate for other interest rates in the market. If banks can earn a risk-free rate on their reserve balances, they will not be willing to lend their funds for a lower rate. This helps to set a minimum benchmark for interest rates in the market.