an open book

• 尽人皆知的事物

an open book的用法和样例：

例句

1. She has fall asleep with an open book in her lap.
   她睡着了,腿上还摊开着一本书。
2. She had fallen asleep with an open book in her lap.
   她睡著了，腿上还摊开著一本书。