What does "blood alcohol concentration" (BAC) refer to?

Blood alcohol concentration (BAC) specifically refers to the percentage of alcohol present in a person's bloodstream. It is a measure that indicates the amount of ethanol in a central volume of blood and is typically expressed as a percentage. For example, a BAC of 0.08% means that there are 0.08 grams of alcohol for every 100 milliliters of blood in the person's system. Understanding BAC is crucial for assessing impairment and legal limits for driving, as laws often set a specific BAC threshold for what constitutes driving under the influence.

The other options do not accurately describe BAC. While the volume of alcohol in a beverage is related to how BAC can be influenced, it does not define what BAC itself is. The duration alcohol stays in the bloodstream pertains to how long it affects the body, which is a different concept. Lastly, the amount of alcohol consumed in a year is unrelated to the immediate measurement of alcohol present in the bloodstream at a specific point in time.