Question

opaque glass is the kind of material ________which you cannot see

Answer 1

Explanation:

Think Shrinky Dinks or stained glass. In contrast, a transparent material allows you to clearly see the objects on the other side. Frosted glass is translucent, and regular glass is transparent. But opaque glass doesn't let any light through at all, and so you can't see through it.

Answer 2

You need to add a preposition through.