Answer:
The answer is d. pyruvate
Explanation:
An oxidizing agent is the substance that gains electrons in a chemical reaction. At the end of the reaction it is reduced and its oxidation state increased.
A reducing agent is the substance that loses electrons in a chemical reaction. At the end of the reaction it is oxidized and its oxidation state decreased.
Pyruvate gains one electron, it is reduced from pyruvate to lactate; thus, pyruvate is the oxidizing agent.
NADH loses one electron, it is oxidized from NADH to NAD; thus, NADH is the reducing agent
