Final answer:
Eating certain foods, body weight, and height are key factors that influence BAC (blood alcohol concentration).
Step-by-step explanation:
The key factor that influences BAC (blood alcohol concentration) is eating certain foods, body weight, and height. When alcohol is consumed, it is absorbed into the bloodstream and affects the BAC, which is influenced by various factors. For example, someone who weighs more may have a lower BAC after consuming the same amount of alcohol as someone who weighs less.