If the Index of Refraction of a Material Is 2,this

If the index of refraction of a material is 2,this means that light travels

A) 2 times as fast in air as it does in vacuum.
B) 2 times as fast in the material as it does in air.
C) 2 times as fast in vacuum as it does in the material.
D) 2 times as fast in the material than it does in vacuum.
E) 1/2 as fast in air as it does in the material.