Given the task definition, example input & output, solve the new input case.
Given scientific fact as input, generate the question from this fact such that it can be answered from the input.
Example: Earth rotates on its axis once times in one day.
Output: How many times does Earth rotate on its axis in one day?
The given output correctly poses a question based on the scientific fact given.

New input case for you: In the freshwater flatworms, protonephridia serve chiefly in osmoregulation.
Output:
In the freshwater flatworms, protonephridia serve chiefly in what?