[nán tí]
difficult problem; a hard nut to crack; aporia; poser; hot potato; facer; headache; stinker; teaser; ticklish problem
set difficult questions
出难题
handle a hot potato
处理难题
How to improve the quality of products was a difficult problem to him.
如何提高产品质量对他来说可是个难题。
The problem looks simple enough, but when you come to try and solve it you'll find it's a real teaser.
这道题看起来很简单， 但当你要解它时你就会发现它确实是一道难题。