Out of the given four waves $(1), (2), (3)$ and $(4)$:
$y = a \sin(kx + \omega t)$ ......$(1)$
$y = a \sin(\omega t - kx)$ ......$(2)$
$y = a \cos(\omega t - kx)$ ......$(3)$
$y = a \cos(kx + \omega t)$ ......$(4)$
emitted by four different sources $S_1, S_2, S_3$ and $S_4$ respectively,interference phenomena would be observed in space under appropriate conditions when:

• A
  Source $S_1$ emits wave $(1)$ and $S_2$ emits wave $(2)$
• B
  Source $S_3$ emits wave $(3)$ and $S_4$ emits wave $(4)$
• C
  Source $S_2$ emits wave $(2)$ and $S_4$ emits wave $(4)$
• D
  $S_4$ emits wave $(4)$ and $S_3$ emits wave $(3)$