"how it got out is a mystery" "it remains one of nature's secrets"
The Mysteries of the Christian Religion.
He remained a mystery in my childhood.
The neurophysiology of language remains almost a total mystery.
Or debate with learned rabbis the mysteries of the Cabbala.
牛津高阶第八版
美国韦氏词典
Dictionary.com
Free Dictionary
维基百科 (自由的百科全书)