D

Glucose residues released from glycogen enter glycolysis as glucose-1-phosphate, which is converted to glucose-6-phosphate without expending the ATP normally used by hexokinase. Thus anaerobic glycolysis from glycogen yields one extra ATP (net 3 ATP) compared with the 2 ATP produced when starting from free glucose [Klahn & Bricker, 1965, PMID 14324976].