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

Example Input: You call the hard case that surrounds the soft parts of some animals the exoskeleton.
Example Output: What do you call the hard case that surrounds the soft parts of some animals?

Example Input: Single-celled organisms and multicellular organisms have this in common: both have a way to get rid of waste materials.
Example Output: Which characteristic do single-celled organisms and multicellular organisms have in common?

Example Input: Acid rain may be caused by air pollution.
Example Output:
Acid rain may be caused by what?