1 Chemistry is a closed book to me.

2 Mathematics has always been a closed book to me.

3 Economics was a closed book to him.

4 I'm afraid physics will always be a closed book to me.

5 Nuclear physics is a closed book to most of us.

6 I'm afraid geophysics is rather a closed book to me.

7 Frank Spriggs was a very able man but something of a closed book.

8 The Shoah will never be a closed book.

9 The kitchenette is a closed book.

10 He is holding a closed book, signifying a mystery, possibly a stage in the alchemical process.

11 Linear preoccupation in the past remains a closed book to modern understanding.

12 I'm not sure what is worse, a closed mind or a closed book. Anthony Liccione 

13 But your own past can be a closed book, even at fourteen.

14 I can not believe that it can be right that this late in the game Poetry is still a closed book.

15 The highly organised St Stephen's Society programme which she now leads was at that time a closed book to her!

16 I tell myself it's a closed book,[] but my cover story becomes an old man's compensation.

17 Final Exam 70 %, all exams are close books and notes.

18 Now, close books, please . Let's sum up the knowledge that we learned in this topic.