An open book （某物）容易理解；（某人）坦诚，没有秘密

open adj. 打开的

My life is an open book.我的生活很简单。

There’s no secret between us, she’s an open book to me.我们之间没有秘密，我对她是了如指掌。

I wish these legal contracts were an open book.我真希望我能读懂这些法律合同。

Adam says he's an open book, but I've seen him sneaking out of his house late at night. Adam说他没什么秘密，但是我看到过他大半夜偷偷溜出他的房间。