Respuesta :
ADP is combined with a phosphate to form ATP in the reaction ADP+Pi+free energy→ATP+H2O. The energy released from the hydrolysis of ATP into ADP is used to perform cellular work, usually by coupling the exergonic reaction of ATP hydrolysis with endergonic reactions.
Your answer is A- Molecules of ATP are converted back to ADP, releasing the energy stored in their phosphate bonds.