When ADP levels are high, glycolysis will be active, and when ATP levels are high, gluconeogenesis is active. So the answer is A. Glycolysis.
Glycolisis requires energy to run, taking a phosphate from ATP, resulting in ADP. it is a part of cellular respiration, glycolysis goes in reverse when gluconeogenesis is active, adding a phosphate group to ADP, turning it back into ATP.
