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) \[y=a\cos (kx+\omega t)\] ......(3) \[y=a\cos (\omega t-kx)\] ......(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 [CPMT 1988]

• 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 waves (4) and \[{{S}_{3}}\] emits waves (3)