How Does the Speed of Light Traveling Through a Medium

Multiple Choice

How does the speed of light traveling through a medium (such as air or glass) compare to the speed of light in a vacuum?

A) It is the same as the speed of light in a vacuum.
B) It is always less than the speed of light in a vacuum.
C) It is always greater than the speed of light in a vacuum.
D) Sometimes it is greater than the speed of light in a vacuum and sometimes it is less, depending on the medium.
E) Light can't travel through a medium; it only can go through a vacuum.