Light Enters a Plane-Parallel Block of Glass from the Vacuum

Multiple Choice

Light enters a plane-parallel block of glass from the vacuum of space and leaves again into space through the opposite side (e.g., in a space-borne instrument) . What is the speed of light after it leaves the glass?

A) same speed as it had before it entered the glass
B) The exit speed will depend on the thickness of the glass, becoming slower the thicker the glass.
C) faster than when it entered because it has passed through the dense glass
D) slower because it has passed through the glass and been slowed by it