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In a completely different vein , " Hugh the Drover " , an opera in two acts by Ralph Vaughan Williams first staged in 1924 , is also sometimes referred to as a " ballad opera " .
 Hugh the Drover, Ralph Vaughan Williams
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:
 Hugh the Drover, Ralph Vaughan Williams