to be +形容词的用法

to be +形容词的用法请问这句话语法怎么分析It is very nice of you to be so considerate.这句话中 to be so considerate 即 to be+形容词是句子的逻辑作主语吗?这句话下面的改写方法对吗？有不妥，忘指教，1.You are to be so considerate is very nice.（不定式作表语）2.To be so considerate is very nice of you （好象不对，是吗)