hard一个特别的用法：充当表语的hard 之后的动词不定式通常表被动含义，或者说句子的主语通常是动词不定式所表示动作的客体。如：
Our traveller's behaviour on the journey is hard to explain
我们的旅客一路上的行为让人很难解释。
The idea of a parallel universe is hard to grasp.
认为另有一个平行宇宙的概念是很难理解的。
Lindsay, like his films, is hard to categorise.
林赛这个人和他的电影一样，很难归类。
This classical poem is hard to understand.
这首古诗很费解。
This medicinal herb is hard to come by.
这种草药很难得。
In rural France, English language magazines are rather hard to come by.
在法国乡村，很难找到英语杂志。
He is hard to deal with.
他这个人难以应付。
The sea of hatred [ regrets] is hard to fill up.
恨海难填。
This hill is hard to climb.
这山很难爬。
For centuries, salt was also hard to get.
几个世纪以来,盐也是很难得到的。
He was hard to convince.
他很难被说服。（很难使他相信。）
Sometimes reality and fantasy are hard to distinguish.
有时候现实和幻想很难区分。
Students are hard to handle.
学生难管。
Secrets are hard to keep.
秘密是很难被保住的。
Deep feelings are hard to put into words.
深厚的感情难以言述。
Because of lack of experience, mistakes are hard to avoid.
经验不足，难免会有失误。
Horses are easy to tame while tigers are hard to tame.
驯马容易，驯虎难