Which two systems are most directly involved in providing molecules needed for the synthesis of fats in human cells?

Out of the following given choices;

a) digestive and circulatory

b) excretory and digestive

c) reproductive and circulatory

d) immune and muscular.

The answer is A. The main precursor of  fatty acids synthesis is acetyl-CoA. It can be formed from the respiration of carbohydrates in the glycolytic pathway.   The other precursor is NADPH and NADH which are reducing factors in the body. They require H+ ions. H+ is regulated by the circulatory/respiratory system as pH of blood is regulated.

both anaerobic and aerobic respiration use glucose (or other carbohydrates), proteins and lipids to produce atp and nadh. cell uses those energy molecules, obtained from food and   breaks them down during the chemical reactions of respiration. in anaerobic respiration, nadh is regenerated to nad+ by enzymes lactate dehydrogenase (lactate is produced, e.g. in muscle cells) or by alcohol dehydrogenase where ethanol is produced (alcohol fermentation), while in aerobic respiration, electrons from nadh are deposited in the mitochondria to regenerate nad+ (electron transport chain. anaerobic respiration produces 2 atp per molecule of glucose compared to aerobic respiration where about 38 atp molecules are produced.

i think that c)gold was found there

but i am not sure