In most states the illegal blood alcohol content for those over 21 is:

• A. .10 or greater
• B. .06 or greater
• C. .08 or greater
• D. .12 or greater

Answer: (C)

The main idea is the legal threshold for impairment when driving. For adults 21 and older, most states set the limit at 0.08% blood alcohol concentration. If a driver's BAC is at or above 0.08, they’re considered legally impaired to operate a vehicle, which means authorities can charge them with driving under the influence regardless of other signs of impairment. This standard is widely used because research shows significant decline in driving abilities—like reaction time, coordination, and judgment—around this level, making it a practical and enforceable line.

That’s why 0.08 or greater is the best answer. The other numbers don’t reflect the common baseline for adult drivers in most states: some places used different limits in the past or have stricter rules for certain groups (like commercial drivers), but for the general adult population, 0.08 is the standard.