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

Input: Consider Input: Fractional crystallization is the separation of compounds on the basis of their solubilities in a given solvent.

Output: What is the separation of compounds on the basis of their solubilities in a given solvent?

Input: Consider Input: A bow wake is created when the wave source moves faster than the wave propagation speed.

Output: What is created when the wave source moves faster than the wave propagation speed?

Input: Consider Input: Hydropower is the most widely used form of renewable energy in the world.
Output: What is the most widely used form of renewable energy in the world?