Given scientific fact as input, generate the question from this fact such that it can be answered from the input.

The behavior of ideal gases is explained by kinetic molecular theory.
The behavior of ideal gases is explained by what theory of gases?

When light passes from one medium to another, it changes speed.
When light passes from one medium to another, it changes what?

In a tropical rainforest, understory are ferns common.

In a tropical rainforest, where are ferns common?