Answer:
3 because when filled in there will be a total of 3 a's
Cellular respiration is the metabolic process by which a cell produces usable energy in the form of ATP. In order to accomplish this cells require Glucose and Oxygen to form the reaction which produces ATP and the byproducts of Water and CO2.
In reality its a complex topic however this is the basic form.
Ayo i think the answer is B, 10 mg/l. bc you would label the respiration rate as R, we come up with a neat little formula: NPP = GPP - R. hope this helps, have an amazing day :)