OPTIONS: (1). chlorofluorocarbons. (2). water vapor. (3). graptolites. (4). hydrogen chloride. (5). deoxyribonucleic acid. (6). flow of electrons. (7). Calcium carbonate. (8). an object.
Given those answer options, answer the question: You are presented with the quiz "what will expand when heated?" But you don't know the answer, so you turn to your teacher to ask for hints. He says that "if gas is heated then that gas will expand" and "hydrogen chloride is a gas". So, what's the best answer to the question?
A:
(4).