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

Input: Consider Input: 10 million years long can a large star be on the main sequence stage.

Output: How long can a large star be on the main sequence stage?

Input: Consider Input: You call the hard case that surrounds the soft parts of some animals the exoskeleton.

Output: What do you call the hard case that surrounds the soft parts of some animals?

Input: Consider Input: An iron nail object is the best conductor of electricity.
Output: Which object is the best conductor of electricity?