Final answer:
Pyruvic acid is produced by glycolysis, which is the first stage of cellular respiration where glucose is converted into pyruvate.
Step-by-step explanation:
During the metabolic pathway called cellular respiration, pyruvic acid is the product of glycolysis. Glycolysis is a series of reactions where glucose is broken down in the cytoplasm, leading to the production of pyruvic acid (pyruvate), with accompanying production of NADH and ATP. The pyruvate then enters the mitochondria where it is transformed into Acetyl Coenzyme A (Acetyl CoA) before entering the Citric Acid Cycle (also known as the Krebs cycle).
Therefore, the correct answer to the question is: a. Glycolysis.