介绍:
The first one “An open book”.
“Open” means “打开”， An open book actually means you know everything about the person who just like an open book.
For example:
I&`&m sure she would have told me anything I wanted to know because she strikes me as AN OPEN BOOK.
我相信她告诉我了关于她的一切，因为我和她一见如故。
“An open book”它的反义词A CLOSED BOOK.
So here it means something we don’t know.
For example:
She is smart, although we talk with each other, she is still “a closed book” for me.
The second one “Read someone like an open book”
“Read someone like an open book” is for the situation when we don’t know what they are thinking about , and it’s easy for us to get it.
For example:
I can “READ HIM LIKE AN OPEN BOOK”，but I know we won’t be friends.
