It's a difficult one.

这是一个困难的问题。

youdao

The decision to search for birth parents is a difficult one to make.

作出寻找亲生父母的决定是困难的。

youdao

Curiosity, he argues, is the third key factor—and a difficult one to preserve.

他认为，好奇心是第三个关键因素，也是一个很难保持的因素。

youdao

He says the process of sorting through those areas, which include sites around the country,but concentrated in the mountainous northern areas, will be a long and difficult one, though it is work that needs to be done in the name of the victims' families.

VOA: standard.2009.12.18

And it's also, it's a really difficult one.

当然也是最难的一个。

韩国人经常犯的失误 - SpeakingMax英语口语达人

The first study, the one with the deceptive dolls with the big shoes and little shoes, is actually fairly difficult.

第一个研究用了有欺骗性的,穿着大鞋和小鞋的洋娃娃,实际上是非常难的

耶鲁公开课 - 心理学导论课程节选

Maybe some other bands should try and do the same, but it's a difficult one.

BBC: Rolling Stones: What is a fair price for a concert ticket?

The past year has been a difficult one, where our beliefs have been tested.

CNN: Powell: Americas dissatisfied with pace of reforms

His father says he knows that the transplant issue is a difficult one for families.

CNN: Boy not allowed to get life-saving transplant in Japan