How Should That Portion of Investment Income Earned from the Investment

How should that portion of investment income earned from the investment of endowment contributions that is required to be used to maintain the purchasing power of the endowment be accounted for if the not-for-profit organization uses the restricted fund method of reporting and has an endowment fund?

A) As investment income in the general fund.
B) As investment income in the endowment fund.
C) As a direct increase in net assets in the general fund.
D) As a direct increase in net assets in the endowment fund.