The answer is D; homeostasis allows the maintenance and regulation of stability and constancy that is needed to properly function. It is found in cells, tissues and organisms,
ATP is adenosine triphosphate, it is like a fully charged battery in a cell, ADP is basically ATP that has been drained of its energy from a chemical reaction. It is like a dead battery that can be recharged later ;)
I swear it's the cell membrane.. I'm not sure though
