Explanation
Interest income distribution is a type of income that a mutual fund pays to its investors from the interest earned on its fixed-income investments, such as bonds and mortgages. Interest income distribution is taxed as ordinary income at the investor's top marginal tax rate, which is the highest tax rate that applies to their income bracket. Therefore, B is the correct answer. References: Interest Income and Taxes - Fidelity, Topic No. 403, Interest Received | Internal Revenue Service