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

Example Input: Processing of filtrate in the proximal tubule helps maintain the ph level in body fluid.
Example Output: Processing of filtrate in the proximal tubule helps maintain what level in body fluid?

Example Input: Sodium-potassium pumps help nerve cells establish a voltage across their plasma membranes.
Example Output: Sodium-potassium pumps help nerve cells establish a voltage across their what?

Example Input: Goldfish, tuna, salmon, perch, and cod are examples of ray-finned fish group of fish.
Example Output:
Goldfish, tuna, salmon, perch, and cod are examples of which group of fish?