艰苦的英文：
difficult
hard
arduous

参考例句：

A laborious task
艰苦的工作

To work strenuously;toil.
辛劳艰苦地工作

Live a rugged life
过艰苦的生活

That was a stiff climb.
那是一次艰苦的攀登。

Hardship allowance
艰苦地区补贴

A tough game,assignment,problem,journey
艰苦的比赛、困难的任务、难题、艰辛的旅程.

A strenuous test of ability and endurance.
考验能力和毅力的艰苦测验

They toiled all day digging the trench.
他们整天艰苦地挖壕沟。

Two years of hard work came to fruition at the commencement
两年来的艰苦学习在毕业典礼时结出了果实。

In his childhood he had suffered from the scanty living consequent upon bad times, and improvident habits
他在儿童时代，一定为了工业不景气和缺乏精打细算的习惯，曾经度过艰苦的生活。

difficult是什么意思：
adj. 困难的；执拗的；不易相处的

The exercise is that difficult!
练习题那么难！

You must admit the task to be difficult [ that the task is difficult ].
你应当承认这项任务是艰巨的。

You must admit the task to be difficult [that the task is difficult].
你必须承认这项任务是困难的。

hard是什么意思：
adj. 硬的，坚固的；困难的；有力的；冷酷无情的
adv. 努力地；困难地；严重地，猛烈地

It is hard to conclude.
这很难断定。

It is blowing hard.
风刮得很大。

It was sleeting hard.
雨雪霏霏。

arduous是什么意思：
adj. 费力的，辛勤的，险峻的

Success is the fruit of arduous striving.
成功是奋斗的结果。

They are very glad that they have been assigned the most arduous task .
他们很高兴被派给最艰巨的任务。

His timidity disinclined him from such an arduous enterprise
他的怯懦使他不愿从事一项如此艰巨的事业。