Four light waves are represented by
(i) y = a1sin ωt.
(ii) y = a2sin(ωt. + ∈)
(iii) y = a1sin 2ωt.
(iv) y = a2sin 2(ωt + ∈).
Interference fringes may be observed due to superposition of
(a) (i) and (ii)
(b) (i) and (iii)
(c) (ii) and (iv)
(d) (iii) and (iv).