As shown, light falls on a mirror at an angle of $45^\circ$. The mirror may be turned about an axis into the page through point X. It is then rotated until the light is reflected back along its original path. Through what angle is the mirror rotated?
- A$22.5^\circ$ clockwise
- B$22.5^\circ$ anticlockwise
- C$45^\circ$ clockwise
- D$45^\circ$ anticlockwise