82591
Christoph Willibald Gluck thought that both " opera buffa " and " opera seria " had strayed too far from what opera should really be , and seemed unnatural .
 Christoph Willibald Gluck
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:
 Christoph Willibald Gluck