Four light waves are represented by:
$(i)$ $y = a_1 \sin \omega t$
(ii) $y = a_2 \sin (\omega t + \phi)$
(iii) $y = a_1 \sin 2\omega t$
(iv) $y = a_2 \sin 2(\omega t + \phi)$
Interference fringes may be observed due to the superposition of:

• A
  $(i)$ and $(ii)$
• B
  $(i)$ and $(iii)$
• C
  $(iii)$ and $(iv)$
• D
  $(i)$ and $(ii)$ as well as $(iii)$ and $(iv)$