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

[EX Q]: Sodium-potassium pumps help nerve cells establish a voltage across their plasma membranes.
[EX A]: Sodium-potassium pumps help nerve cells establish a voltage across their what?

[EX Q]: Plasma membranes encloses and defines the borders of cells.
[EX A]: What encloses and defines the borders of cells?

[EX Q]: Water takes the form of ice on planet mars.
[EX A]:
What form does water take on the planet mars?