difficult problem可数的。
difficult ：adj. 困难的; 费力的; 难做的; 难解的; 问题很多的; 充满艰难困苦的; 麻烦的; 难以讨好的; 难以取悦的; 不愿帮助的。
problem：n. 问题; 难题; 棘手的问题; 困难; 逻辑题; 数学题。
扩展资料
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。
She is working at a difficult problem in mathematics.
她在做一道数学难题。
How to grow rice in a dry area is a difficult problem.
在干旱地区种水稻可是一个难题。
When you come across a difficult problem, think about it by yourself first.
遇到难题的时候先自己想想。
The student decided to work out the difficult problem by himself.
这个学生决心独自解决这道难题。
Air pollution is a difficult problem for environmental protect.
城市大气污染问题是环境保护的一项难题。
