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

Ex Input:
Light retains its original color under water because frequency remains the same when light is refracted.

Ex Output:
Light retains its original color under water because what remains the same when light is refracted?


Ex Input:
Very low density is the concentration of gas molecules in the mesosphere.

Ex Output:
What is the concentration of gas molecules in the mesosphere?


Ex Input:
Heat is produced when paper is burned.

Ex Output:

Which form of energy is produced when paper is burned?