What is the most accurate way to determine a person's level of intoxication?

Answer: C — Determining the person's blood alcohol concentration (BAC)

Determining a person's blood alcohol concentration (BAC) is the most accurate way to determine their level of intoxication. BAC is measured by the amount of alcohol in a person's blood and is considered the standard measurement of intoxication. Option A of passing a coordination test is subjective and can vary based on factors such as a person's physical ability and the difficulty of the test. Option B of judging by the look of someone's eyes can also be subjective and can be affected by factors such as fatigue and allergies. Option D of asking simple questions may not accurately reflect a person's level of intoxication as they may be able to answer questions coherently but still have a high BAC. Therefore, the most reliable way to determine a person's level of intoxication is by calculating their BAC.