Hold an open book in your hands in front of you and close it quickly. What can you feel?

手中拿一本展开的书放在面前，快速合上书，你能感觉到什么？

I saw an open book on the table.

我看见在桌子上书是打开的。

Childhood is an open book.

童年是一本打开的书。

Is it an open book exam?

那是开卷考试吗？

There is an open book.

那有一本打开的书。