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

Toxins is contained in the skin of brightly colored poison dart frogs.
What is contained in the skin of brightly colored poison dart frogs?

Light retains its original color under water because frequency remains the same when light is refracted.
Light retains its original color under water because what remains the same when light is refracted?

Earthquakes mark the motions of colliding plates and the locations where plates plunge into the mantle.

Earthquakes mark the motions of colliding plates and the locations where plates plunge into what?