To determine if sides \( AC \) and \( BC \) are constructed as copies of side \( AB \), Reza needs to verify that the lengths of these sides are equal. The correct response to this requirement is:
Reza must use his compass to measure side \( AB \) to see if \( BC \) and \( AC \) are the same length.
This option directly addresses the need to verify the lengths of the sides using a compass, which is a tool commonly used to measure distances in geometric constructions.