Separation of Cu, Zn and sulphur has been a difficult problem for a long time.

铜锌硫多金属矿石分离历来是选矿界的难题。

youdao

How to keep on talent has been a difficult problem of state enterprise human resources management.

如何留住人才成为国企人力资源管理中的一大难题。

youdao

Separation of copper, zinc and sulphur complex ore has been a difficult problem in the mineral processing field.

前言： 铜锌硫多金属矿石分离一直是选矿界的难题。

youdao

And this is a very, very difficult problem -- there is no question -- and it has been a problem that previous Presidents have worked to resolve.

WHITEHOUSE: Press Briefing

Once a problem has been defined by a category of solution it is difficult to break out of that category.

FORBES: SMAP: Solutions Masquerading as Problems