I think your talking about the lungs
External parts of the pig
Biology or Geology. These answers make the most sense to me.
The carbon cycle. Although it's not specific, it talks about combustion or respiration. The reason I chose the carbon cycle, is because nitrogen DOES appear in photosynthesis, but you were strictly talking about carbohydrates.
The right answer is: <span>A
<span>A biogeochemical cycle is the process of transport and cyclic transformation of a chemical element (like oxygen, carbon or azote) or a compound between the large reservoirs that are the geosphere, the atmosphere, the hydrosphere, in which the biosphere is found.
</span>The three elements are able to exist in a gaseous form in the atmosphere to complete their respective natural cycle.</span>