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It also preserved much of the medieval structure of the Mass - stone altars remained , the clergy wore traditional vestments , much of the service was sung , and the priest was instructed to put the communion wafer into a communicant 's mouth instead of in their hand .
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Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
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