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

Ex Input:
Oil is the most commonly used source of energy in the world.

Ex Output:
What is the most commonly used source of energy in the world?

Ex Input:
Just as salty taste involves perception of sodium ions in saliva, sweet taste correlates with presence of glucose.

Ex Output:
Just as salty taste involves perception of sodium ions in saliva, what taste correlates with presence of glucose?

Ex Input:
Transmembrane proteins span the entire plasma membrane.

Ex Output:
What proteins span the entire plasma membrane?