Alabama CDL Class A Permit Practice Test

Blood alcohol concentration is determined by how alcohol is distributed in the body's water, which depends on body size. A person with more body mass has more body water to dilute the alcohol, so the same amount of alcohol yields a lower BAC. A lighter person has less body water, so the BAC rises higher for the same amount consumed. That makes weight a necessary piece of information to estimate BAC.

The other options don’t affect the amount of alcohol in the bloodstream in a direct way: favorite color has no physiological impact, time of day isn’t enough by itself to determine BAC without knowing how much and when alcohol was consumed, and driving speed doesn’t change how alcohol is distributed in the body.