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Their modern derivations include yearbook s , friendship book s , and guest book s. They were popular among university students from the 15th century until the mid-19th century , after which their popularity began to wane as they were gradually replaced by yearbooks .
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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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