Two Parallel Glass Plates of Index of Refraction N Are $\lambda$

Multiple Choice

Two parallel glass plates of index of refraction n are separated by an air film of thickness d. Light of wavelength $\lambda$ in air, normally incident on the plates, is intensified on reflection when, for some integer m

A) 2d = m $\lambda$
B) 2d = m $\lambda$ 0/n
C) 2d = mn $\lambda$
D) 2d = (m + 1/2) $\lambda$
E) 2nd = m $\lambda$ /2