A prism is constructed from transparent plastic. Within this plastic, light moves at $0.80c$, where $c$ denotes its speed in air. As illustrated, light strikes one face of the prism at right-angles. The light just manages to leave the sloping face of the prism. What is angle $\theta$?
- A$37^\circ$
- B$39^\circ$
- C$51^\circ$
- D$53^\circ$