a closed book a thing of which you have no knowledge or understanding.
1944Frank CluneThe Red Heart The desert is an open book to the man of the Vast Open Spaces, but to the schoolmaster it was a closed book.
英语词组固定搭配大全包含15956条英汉双解词组，基本涵盖了全部常用英文词组、短语的翻译及用法，是英语学习的有利工具。