if you must knowspoken used when you answer a question that you think someone should not have asked, because it is slightly impolite 如果你非要知道用于回答认为别人不该问的问题，因为提这个问题不太礼貌〕 Well, if you must know, I’m thirty-six. 好吧，如果你非要知道，我三十六岁了。
if you must know• April 14, if you must know.• But I was extremely jealous of him, if you must know.• I had a bad dose of influenza, if you must know.• It's my sister Rose's birthday on Sunday, if you must know.• More than enough, if you must know.• But if you must know, Mrs. Jewkes was present.
→ if you must know at must1(5)