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Following the Russian Revolution , the Russian SFSR became the largest and leading constituent of the Soviet Union , the world 's first constitutionally socialist state .
 Russian Revolution, Russian SFSR, Soviet Union
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:
 Russian Revolution, Russian SFSR, Soviet Union