What is the reason carbon atoms are the most versatile building blocks of the molecules used by living organisms?

• A. Carbon is the central atom of carbon dioxide, a necessary molecule for photosynthesis.
• B. Carbon is the central atom in urea, a molecule used by many living organisms to transport wastes from the body.
• C. All of the listed responses are correct.
• D. Each carbon atom acts as an intersection point from which a molecule can branch off in up to four directions.