In what circumstance would an investor receive a T3 or T5 reporting a capital gain...

A T3 or T5 slip reporting a capital gain is issued when an investor sells their mutual fund units at a profit, not when the fund itself realizes gains. The feedback from the document states:

"In the normal course of portfolio management, shares are bought and sold either at a gain or at a loss for the fund. By the end of the year, many funds will have generated net capital gains on their portfolio transactions. The capital gains are distributed in the form of a capital gains dividend reported on a T5 or T3." However, for the investor, the correct answer is A, as clarified by standard tax rules: capital gains are realized by the investor upon selling units at a price higher than their average cost.