Answer the following question given this paragraph: The opening image is a model of an important chemical compound. Without it, living things would not have the energy they need to survive. Compared with most other compounds in living things, molecules of this compound are small and simple. In the model, the gray circles represent carbon atoms, the red circles represent oxygen atoms, and the black circles represent hydrogen atoms. Q: An important chemical compound, which supplies living things with the energy they need to survive, is composed of carbon, oxygen and atoms of what other element? Choices: - magnesium - nitrogen - calcium - hydrogen A:
Answer:
hydrogen