122300
Such concerts were crucial to the formation of youth identity in the U.S. during a time of social revolution , and have continued to represent elements of society frequently seen as " rebellious , " especially against the strictures of mid-twentieth-century social normativities .
 U.S.
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: media, plant, vehicle, astronomical object, time, disease, animal, location, person, organization, mythical figure, food, biology, geographical phenomenon, instrument, event 
Text: {0} 
Answer:
 U.S.