incorporation of carbon through digestion into animal tissues release of carbon into the atmosphere while breathing atmospheric carbon incorporated into sugars in plants breakdown of carbon in plant tissues to form oil
I gave my students this multiple choice question: Carbon cycles through various reservoirs on Earth. The time it takes to form these reservoirs varies greatly. Which process in the carbon cycle takes millions of years to form the indicated reservoir?

Only one answer is correct among these 4 choices:
- incorporation of carbon through digestion into animal tissues
- release of carbon into the atmosphere while breathing
- atmospheric carbon incorporated into sugars in plants
- breakdown of carbon in plant tissues to form oil

Could you tell me which one is correct?

breakdown of carbon in plant tissues to form oil