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

Example Input: Certain air pollutants form acid liquid when dissolved in water droplets in the air.
Example Output: Certain air pollutants form which liquid when dissolved in water droplets in the air?

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: Multiple genes mutations is usually necessary to develop cancer.
Example Output:
What is usually necessary to develop cancer?