When a Beam of Light That Is Traveling in Glass $60 ^ { \circ }$

When a beam of light that is traveling in glass strikes an air boundary at the surface of the glass, there is

A) a $60 ^ { \circ }$ phase change in the reflected beam.
B) a $180 ^ { \circ }$ phase change in the reflected beam.
C) no phase change in the reflected beam.
D) a $90 ^ { \circ }$ phase change in the reflected beam.
E) a $45 ^ { \circ }$ phase change in the reflected beam.