What is the reason for interference?  (Explain)
a)Phase difference               c)Change of velocity
b)Change of amplitude        d)Intensity

Dear Student , interference is a phenomenon in which two waves superpose to form a resultant wave of greater, lower, or the same amplitude also reason for interference is superposition of two waves in same direction , it totally depends on phase difference whether it will be constructive or destructive . Hence answer is option (a). Regards!