instruction:
Given scientific fact as input, generate the question from this fact such that it can be answered from the input.
question:
Fractional crystallization is the separation of compounds on the basis of their solubilities in a given solvent.
answer:
What is the separation of compounds on the basis of their solubilities in a given solvent?

question:
Age causes reduction of elasticity in all organs.
answer:
What causes reduction of elasticity in all organs?

question:
An exploding firework is seen before it is heard observation demonstrates that light waves travel much faster than sound waves.
answer:
Which observation demonstrates that light waves travel much faster than sound waves?