The answer is A.Composition
Why is (A) the answer?
When we look into the chemical definition of Composition, it says that it all refers to the way the atoms are arranged or of the type of the atoms in molecules of chemical substances.
The chemical composition varies (which also means it changes) when other chemical changes happen/occur in chemicals.
And as well we are making a total new substance when we give it a change chemically.
So in conclusion, a chemical change is a change in the COMPOSITION of a substance