Answer the following question given this paragraph: 

Total internal reflection occurs when light goes from a slow (high index of refraction) medium to a fast (low index of refraction) medium. With total internal reflection, light refracts so much it actually refracts back into the first medium. This is how fiber optic cables work: no light leaves the wire.


Q: When does internal reflection occur?

 Choices:

- when light goes from a slow medium to another slow medium

- when light goes from a fast medium to a slow

- when light goes from a fast medium to another fast medium

- when light goes from a slow medium to a fast

A:
when light goes from a slow medium to a fast
