A General Condition for Two Coherent Waves to Undergo Constructive

Multiple Choice

A general condition for two coherent waves to undergo constructive interference is that

A) their phase difference is zero.
B) their phase difference is π/2 rad.
C) their phase difference is ±π/2 rad.
D) their phase difference is an even integral multiple of π rad.
E) their phase difference is an odd integral multiple of π rad.