What is the average alcohol content per 12-ounce beer bottle produced by Boston Beer Company?
SELECT AVG(T1.abv) FROM beers AS T1 INNER JOIN breweries AS T2 ON T1.brewery_id = T2.id WHERE T2.name = 'Boston Beer Company' AND T1.ounces = 12
database name:db_id craftbeer
Breweries table Breweries Cols: id dtype integer, name dtype text, city dtype text, state dtype text, 
Beers table Beers Cols: id dtype integer, brewery id dtype integer, alcohol by volume dtype real, International Bitterness Units dtype real, name dtype text, style dtype text, ounces dtype real, 
