closed book
US /kloʊzd bʊk/
UK /kləʊzd bʊk/
成语
天书, 不为人知的事
a subject or person about which one knows nothing or very little
示例:
•
Quantum physics is a closed book to me.
量子物理学对我来说是本天书。
•
His past is a closed book; he never talks about it.
他的过去是本天书；他从不谈论它。