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English definition of “closed book”

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closed book

noun [S] uk   informal us  
a subject about which you know or understand nothing: I'm afraid physics will always be a closed book to me.
Translations of “closed book”
in Chinese (Traditional) 一無所知的學科,完全不懂的學科…
in Chinese (Simplified) 一无所知的学科,完全不懂的学科…
(Definition of closed book from the Cambridge Advanced Learners Dictionary & Thesaurus © Cambridge University Press)
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