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

Input: Consider Input: Natural resource type of resource is limited in supply and cannot be replaced except over millions of years.

Output: What type of resource is limited in supply and cannot be replaced except over millions of years?

Input: Consider Input: Sodium-potassium pumps help nerve cells establish a voltage across their plasma membranes.

Output: Sodium-potassium pumps help nerve cells establish a voltage across their what?

Input: Consider Input: Co 2 is the molecular formula of carbon dioxide.
Output: What is the molecular formula of carbon dioxide?