Two narrow slits, of width a, separated by a distance d, are illuminated by light with a

Question:

Two narrow slits, of width a, separated by a distance d, are illuminated by light with a wavelength of 660 nm. The resulting interference pattern is labeled (1) in the figure. The same light source is then used to illuminate another group of slits and produces pattern (2). The second slit arrangement is

(a) Many slits, spaced d apart.
(b) Many slits, spaced 2d apart.
(c) Two slits, each of width 2a, spaced d apart.
(d) Two slits, each of width a/2, spaced d apart.