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

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: Carbon atoms have six neutrons as well as six protons.
Example Output: Carbon atoms have six neutrons as well as how many protons?

Example Input: During phase change, the temperature of a system remains constant.
Example Output:
What happens to the temperature of a system during phase change?