A beam of light from a source `L` is incident normally on a plane mirrorr fixed at a certain distance `x` from the source. The beam is reflected back as a spot on a scale placed just above the source `L`. When the mirrorr is rotated through a small angle `theta`, the spot of the light is found to move through a distance `y` on the scale. The angle `theta` is given by `:`
A. `y/x`
B. `x/(2y)`
C. `x/y`
D. `y/(2x)`
