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

Example Input: The sun and the moon appear to be about the same size in the sky because the moon is smaller in diameter and is closer to earth than the sun.
Example Output: Which statement best explains why the Sun and the Moon appear to be about the same size in the sky?

Example Input: A bow wake is created when the wave source moves faster than the wave propagation speed.
Example Output: What is created when the wave source moves faster than the wave propagation speed?

Example Input: Radiation, chemicals, and infectious agents are types of mutagens.
Example Output:
Radiation, chemicals, and infectious agents are types of what?