closed book

n. 不为人知的人或事, 无法解释的事物

例句与用法：

Fishing is a closed book to me.

我对钓鱼是一窍不通。

Nuclear physics is a closed book to me.

核物理学是我完全不懂的一门学科。

Nuclear physics is a closed book to most of us.

我们大多数人对原子核物理学一窍不通。