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

Input: Consider Input: The bird ancestor that lived in trees developed wings, which is commonly associated with birds.

Output: The bird ancestor that lived in trees developed what feature commonly associated with birds?

Input: Consider Input: The metallic bond is responsible for the properties of metals.

Output: What is responsible for the properties of metals?

Input: Consider Input: Remains unchanged happens to the mass number during a nuclear decay process by positron emission.
Output: What happens to the mass number during a nuclear decay process by positron emission?