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

Q: Cells are the basic building blocks of the human body.

A: What are the basic building blocks of the human body?
****
Q: Natural resource type of resource is limited in supply and cannot be replaced except over millions of years.

A: What type of resource is limited in supply and cannot be replaced except over millions of years?
****
Q: Oil is the most commonly used source of energy in the world.

A:
What is the most commonly used source of energy in the world?
****