A student traces a reflected light ray backward in a straight line until it meets a mirror. Which of the following best explains why this backward tracing reveals the original path of the incident ray?
(a) Because the angle of incidence equals the angle of reflection, extending the reflected ray backward automatically reproduces the incident ray.
(b) Tracing the reflected ray backward locates the virtual image of the light source inside the mirror, so that line must coincide with the incoming ray.
(c) Light rays follow identical paths in either direction when traveling through the same medium.
(d) Momentum perpendicular to the mirror must be conserved, so reversing the reflected ray aligns it with the original incident ray.