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

Example Input: Deep currents are caused by differences in density at the top and bottom of the ocean.
Example Output: What is caused by differences in density at the top and bottom of the ocean?

Example Input: Diffraction is the phenomenon in which light and sound waves become circular at the point source of a barrier.
Example Output: What is the phenomenon in which light and sound waves become circular at the point source of a barrier?

Example Input: The cranium (skull) protect(s) the brain.
Example Output:
What part of the body protects the brain?