Final answer:
The proper noun in the sentence 'Quran is the holy book of Muslims' is 'Quran'. This term refers to a specific book, thus making it a proper noun. It is a unique name of a holy book considered by all Muslims worldwide.
Step-by-step explanation:
In the provided sentence, 'Quran' is the proper noun used. Proper nouns are names that refer to specific people, places, or things. Here the term 'Quran' is a specific book that is considered holy by the followers of Islam.
Proper nouns are typically capitalized in English to set them apart from ordinary nouns. To further explain, if we said 'book' that's a common noun because it could be any book, but if we say 'Quran', we're calling to mind one particular book.
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