Final answer:
The glycolysis and the CAC must occur twice per glucose molecule.
Step-by-step explanation:
The glycolysis and the citric acid cycle (CAC) must occur twice per glucose molecule. In glycolysis, one glucose molecule is split into two molecules of pyruvate, which then enter the CAC. Each pyruvate molecule is converted into one acetyl-CoA molecule, and the CAC runs twice for the two acetyl-CoA molecules derived from one glucose molecule. Therefore, the correct answer is b) Twice.