Which of the following correctly describes a compound?
A. The atoms are chemically bonded together, and they retain their individual physical and chemical properties.
B.The atoms are not chemically bonded, and there is no set ratio for how the atoms can combine together.
C. The atoms can only combine in fixed ratios, and they can only be separated by a chemical change.
D. The atoms do not retain their individual chemical properties, and they can be separated by physical means.