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

Chemical digestion mainly occurs in the small intestine.
Where does chemical digestion mainly occur?

Blood is made up of red blood cells, white blood cells, platelets, and plasma.
Blood is made up of red blood cells, white blood cells, platelets, and what else?

Nitrogen dioxide is a byproduct from the combustion of fossil fuels like coal and gasoline.
What is a byproduct from the combustion of fossil fuels like coal and gasoline?