A CD Is Made with a Plastic Coating with Index $\lambda$

Multiple Choice

A CD is made with a plastic coating with index of refraction n and is used with a laser that produces a wavelength $\lambda$ in the plastic. Which of the following pit depths would produce the desired destructive interference in this situation?

A) " $\lambda$ /2n"
B) " $\lambda$ /4"
C) " $\lambda$ /4n"
D) " $\lambda$ /2"