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He also appeared at the Royal Opera House in London 's Covent Garden , the Monte Carlo Opera , the Liceo in Barcelona and other European venues .
 Royal Opera House, Covent Garden, Opera
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Royal Opera House, Covent Garden, Opera