In a Young double slit experiment, green light is incident on the two slits. The interference pattern is observed on a screen. Which one of the following changes would cause the observed fringes to be more closely spaced?
[Figure: Diagram showing incoming light waves hitting two slits and creating fringes on screen]
(a) Reducing the separation between the slits.
(b) Using blue light instead of green light.
(c) Using red light instead of green light.
(d) Moving the light source further away from the slits.