How to improve the quality of products was a difficult problem to him.
如何提高產(chǎn)品質(zhì)量對(duì)他來說可是個(gè)難題。
She is working at a difficult problem in mathematics.
她在做一道數(shù)學(xué)難題。
How to grow rice in a dry area is a difficult problem.
在干旱地區(qū)種水稻可是一個(gè)難題。
When you come across a difficult problem, think about it by yourself first.
遇到難題的時(shí)候先自己想想。
The student decided to work out the difficult problem by himself.
這個(gè)學(xué)生決心獨(dú)自解決這道難題。
Air pollution is a difficult problem for environmental protect.
城市大氣污染問題是環(huán)境保護(hù)的一項(xiàng)難題。