The biological macro molecule is CARBOHYDRATE.
Carbohydrates are made up of just three elements, which are carbon, hydrogen and oxygen, all joined together in a ringed structure. The number of carbon a carbohydrate has determined the class of carbohydrate under which it is grouped. The particular one we are given in this question has five carbon, so it is a pentose sugar.
Carbohydrate are the major source of energy in the living cells.
C: carbon and oxygen cycles are the most closely related in their role in sustaining life because they both include processes of exchanging themselves among different parts of the earth. E.g. they both process through the ground, in the air, etc.
I would believe that sugars and starches would have the most caloric value.