The problem of hunger worldwide is a hard nut to crack. I'm afraid that scientists need to put in more efforts.

全球性的饥饿问题是个棘手的问题，恐怕科学家们需要付出更多的努力。

youdao

Sometimes, it is a hard nut to crack without an expert's help.

有时候，如果没有专家的帮助，这是一件很难解决的事情。

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Building such a bridge over the bay was a hard nut to crack but the local government made it within two years.

在海湾上建造这样一座桥是一件困难的事情，但当地政府在两年内完成了。

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At first, the obsession with conventional degrees will be a hard nut to crack.

FORBES: Free Education Is A Meme Whose Time Has Come

England scented a rout, but found the sixth-wicket combination of Mashud and Mushfiqur a hard nut to crack.

BBC: SPORT | Cricket | Ban v Eng 2003 | England take control

Many companies have tried and failed to break the US market, but it has proved a hard nut to crack for UK retailers.

BBC: US Tesco brand Fresh & Easy 'wasn't aspirational'