Superposition of Waves Quiz (1) Physics AS Level

Light of a single wavelength is incident normally on a double slit. The slit separation can be varied.
A screen is placed a fixed distance away from the double slit. The screen and double slit are parallel. A pattern of bright interference fringes is observed on a screen.
Which graph best shows the variation of the separation $x$ of the bright interference fringes with the slit separation $a$?