Monochromatic (single wavelength) light passes through a single slit of width a and falls onto a screen that is a distance L away. Looking at the light on the screen, there is a central bright region centered directly across from the middle of the slit. The central bright region is bounded on each side by a first-order minimum, so its width is 2y. Which of the following changes would decrease the width of the central bright region?

a. increasing L, the distance between the slit and the screen

b. decreasing the wavelength of the light

c. decreasing a, the slit width

d. all of the above