Answer
Layer B
Work Step by Step
According to the Review & Summary on page 999: "Total Internal Reflection: A wave encountering a boundary across which the index of refraction decreases will experience total internal reflection if the angle of incidence exceeds a critical angle $\theta_c$..."
Note that for total internal reflection to occur, the wave must encounter a boundary across which the index of refraction decreases.
For total internal reflection to occur on both sides of a layer in Figure 33-32, the layer must be bounded on both sides by layers with a lower index of refraction. Only layer B satisfies this criteria.
