A retroreflector consists of two flat mirrors joined at a right angle (\(90^\circ\)), as shown in the diagram. A light ray traveling in a plane perpendicular to both mirrors strikes Mirror 1 at an angle of incidence \(\theta_1\) relative to the surface normal, where \(0^\circ < \theta_1 < 90^\circ\). The ray reflects off Mirror 1, strikes Mirror 2 at an angle of incidence \(\theta_2\), and then exits the system. Which of the following statements and justifications correctly explains why the exiting ray is always parallel to the incoming ray, regardless of the value of \(\theta_1\)?