1. Which is the main element present in living things?
2. Which are the three different forms of carbon?
3. Which is the hardest substance known?
4. Explain through what process carbon atoms in the air become part of our body.
5. Which are the three processes by which carbon atoms in the body of living things return to the air?
6. What is the greenhouse effect? Why is it happening?
7. In what form is carbon found at the bottom of the sea?