若形容词是描述不定式行为者的性格、品质的,如kind,good,nice,right,wrong,clever,careless,polite,foolish等,用of sb..
It’s very kind of you to help me.你能帮我,真好.
It’s clever of you to work out the maths problem.
你真聪明,解出了这道数学题.
若形容词仅仅是描述事物,不是对不定式行为者的品格进行评价,用for sb.,这类形容词有difficult,easy,hard,important,dangerous,（im）possible等.
It’s very dangerous for children to cross the busy street.
对孩子们来说,穿过繁忙的街道很危险.
It’s difficult for us to finish the work.对我们来说,完成这项工作很困难.
注 意 ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○
of sb.的句型通常都可转换为不定式作状语的句子,但for sb.句型不可以.
It’s very nice of you to offer me a seat.
= You are nice to offer me a seat.十分感谢你给我让座.
It is careless of him to lose so many things.
= He is careless to lose so many things.他丢了这么多东西,真是太粗心了.
It’s very important for you to practise your oral English in daily life.
在日常生活中练习你的英语口语非常重要的.
这句话不能说成：It is very important of you to practise…