In previous years, Boze City had received a $400,000 gift of cash and investments. The donor had specified that the earnings from the gift must be used to beautify city-owned parks and the principal must be re-invested. During the current year, the earnings from this gift were $24,000. The earnings from this gift should generally be considered revenue to which of the following funds?

a) Special revenue fund.

b) Private-purpose trust fund.

c) Agency fund.

d) Permanent fund.