The diagram shows a ray PQ being reflected by mirror X towards a parallel mirror Y. The reflected ray, RS, is parallel to PQ. Which statement is correct?
- AThe angle between PQ and QR is $45^\circ$.
- BThe angle between QR and RS is $180^\circ$.
- CThe angle of incidence of PQ on mirror X is $60^\circ$.
- DThe angle of incidence of QR on mirror Y is $45^\circ$.