Cách sử dụng
The expression "an open book" means that somebody is easy to understand because they are honest and transparent about their thoughts, feelings, and intentions. You can use this expression when talking about somebody who is very open about themselves or who doesn't seem to hide anything from others. For example, if somebody tells you all their secrets and thoughts without hesitation, you could say they are an open book. Or, if somebody's facial expressions are easy to read and you can tell what they are thinking or feeling, you could also say they are an open book.