1) It's a sealed book to me.

2) He is a sealed Book to her.

3) Books were beyond her interest - knowledge a sealed book.

4) Fifteenth - century art was a sealed book to him.

5) The origin of the universe is still a sealed book to us.

6) I know a little Russian, but this is a sealed book to me.

7) The young generation was always something of a sealed book to Mr Smith.