Three Experiments Involving a Thin Film (In Air)are Shown $\lambda$ Denotes the Wavelength of the Light in the Film, Which

Multiple Choice

Three experiments involving a thin film (in air) are shown.If t denotes the film thickness and $\lambda$ denotes the wavelength of the light in the film, which experiments will produce constructive interference as seen by the observer?

A) I only
B) II only
C) III only
D) I and III only
E) II and III only