Two Identical Light Waves, a and B, Are Emitted from Different

Multiple Choice

Two identical light waves, A and B, are emitted from different sources and meet at a point P. The distance from the source of A to the point P is L_A; and the source of B is a distance L_B from P. Which one of the following statements is necessarily true concerning the interference of the two waves?

A) A and B will interfere constructively because their amplitudes are the same.
B) A and B will interfere constructively if L_A = L_B.
C) A and B will interfere destructively if L_A - L_B = m $\lambda$ where m = 0, 1, 2, 3, ...
D) A and B will interfere destructively if L_A is not equal to L_B.
E) A and B will interfere constructively because their wavelengths are the same.