Final answer:
Approximately 10-20% of ethanol is metabolized by CYP2E1, especially during heavy drinking when the microsomal ethanol oxidizing system is more active.
Step-by-step explanation:
About 10-20% of ethanol is metabolized by CYP2E1. The majority of ethanol is processed by the alcohol dehydrogenase system, resulting in the creation of acetaldehyde, which is then rapidly converted to acetate by acetaldehyde dehydrogenase due to its toxicity. However, the microsomal ethanol oxidizing system (MEOS) becomes more prominent in the metabolism of ethanol — particularly during periods of heavy drinking. The MEOS uses enzymes, including CYP2E1, to process ethanol. Thus, the correct answer to the question is d) 2E1.