Blood Alcohol Content is the legal name for BAC but Blood Alcohol Concentration is sometimes used for simpler description. Blood alcohol content is usually expressed as a percentage of ethanol in the blood in units of mass of alcohol per volume of blood or mass of alcohol per mass of blood, depending on the country.
One way that society controls science is that the government can make certain experiments illegal. Hmm, maybe, but the apex answer is: People pass laws to restrict some research.
Controls are a vital part of a science experiment. If at any point, your variable could affect the end result of your experiment, it should be considered the control. Your control may change as your experiment changes. For instance, you may need a different sample to prove a different hypothesis.