The correct answer is B. Compound. Methane is a compound composed of atoms of carbon and hydrogen. A macromolecule is a large molecule composed of smaller molecules, such as proteins, carbohydrates, and lipids. An atom is the smallest unit of matter that can exist and is composed of protons, neutrons, and electrons. An element is a substance that cannot be broken down into simpler substances and is composed of only one type of atom.