How Should Investment Income Earned from the Investment of Endowment

How should investment income earned from the investment of endowment contributions be accounted for if the not-for-profit organization uses the restricted fund method of accounting and the use of the investment income is restricted to a specific purpose for which the not-for-profit organization has a restricted fund?

A) As investment income in the endowment fund
B) As a deferred contribution
C) As investment income in the general fund
D) As investment income in the specific restricted fund