Dart is charged with the statutory offense of "knowingly violating a regulation of the State Alcoholic Beverage Control Board" and specifically that he knowingly violated regulation number 345-90 issued by the State Alcoholic Beverage Control Board. That regulation prohibits the sale of alcoholic beverages to any person under the age of 18 and also prohibits the sale of any alcoholic beverage to a person over the age of 17 and under the age of 22 without the presentation of such person's driver's license or other identification showing the age of the purchaser to be 18 or older. The evidence showed that Dart was a bartender in a tavern and sold a bottle of beer to a person who was 17 years old and that Dart person who was 17 years old and that Dart did not ask for or see the purchaser's driver's license or any other identification. Which of the following, if found by the jury, would be of the most help to Dart? 
The purchaser had a driver's license that falsely showed his age to be 21. Dart had never been told he was supposed to check identification of persons over 17 and under 22 before selling them alcohol. Dart did not know that the regulations classified beer as an alcoholic beverage. Dart mistakenly believed the purchaser to be 24 years old.