[nán tí]
difficult problem; a hard nut to crack; aporia; poser; hot potato; facer; headache; stinker; teaser; ticklish problem
set difficult questions
出難題
handle a hot potato
處理難題
How to improve the quality of products was a difficult problem to him.
如何提高產品質量對他來說可是個難題。
The problem looks simple enough, but when you come to try and solve it you'll find it's a real teaser.
這道題看起來很簡單， 但當你要解它時你就會發現它確實是一道難題。