Animals eat plants, and when they do, they obtain the carbon. Later, they release that carbon by means of respiration. Fungus, Bacteria, Algae and other microorganisms create carbon when they decompose dead plants and animals.
I believe it is use sugar and and release carbon. We breath in oxygen so you know it can’t be anything where we release oxygen. And I don’t know how we could release nitrogen so I would go with the second one
