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

Example Input: Collision theory states that chemical reactions occur when atoms, ions, or molecules collide.
Example Output: What states that chemical reactions occur when atoms, ions, or molecules collide?

Example Input: The seven unique crystal types are defined by faces parts of themselves (parts that intersect at various angles).
Example Output: The seven unique crystal types are defined by what parts of themselves (parts that intersect at various angles)?

Example Input: If two chlorine atoms share their unpaired electrons by making a covalent bond and forming cl2, they can each complete their valence shell.
Example Output:
If two chlorine atoms share their unpaired electrons by making a covalent bond and forming cl2, they can each complete their what?