The most accurate way to determine a person's level of intoxication is to:

Answer: C — Determine the person's BAC

Determining a person's BAC (blood alcohol content) is the most accurate way to determine their level of intoxication because it directly measures the amount of alcohol in their system. BAC can be affected by many factors such as weight, gender, and how much food the person has consumed, making visual cues like coordination or appearance of the eyes unreliable. Asking the person how much they have drunk also relies on their honesty and ability to accurately recall the amount consumed. Therefore, determining BAC through a blood or breath test is the most accurate method.