ATP because its essentially stored energy. All the cell has to do to release the energy is break off a phosphate. ATP is like money in the bank. It's there when cells need energy. Glucose is the preferred molecule to go through the krebs cycle to be made into ATP, but it has to be converted to ATP before its energy can be used. Starch is a macromolecule and has to be broken down into monosaccharides and then converted into ATP, so it's not he most direct source of energy. DNA is the code for telling the cells what proteins to make. It's not a source of energy. Sorry its long but hope it helps!!
