so...that，too...to和enough to是初中英语教材中的重要结构。在一定条件下它们可以相互转换，并经常成为中考热点，请看下面三道中考试题：
1.The water was so dirty that we couldn't drink it.
The water was ____ dirty for us ____ drink.(2001上海市)
2.The child is so young that he can't put on his clothes.
The child isn't ____ ____ ____ put on his clothes.('99四川宜宾)
3.The problem is too difficult for me to work out.
The problem isn't ____ ____ ____ for me to work out.(2001重庆市)
由分析可知答案为：1.too，to 2.old enough to 3.easy enough
那么在什么情况下三者可以相互转换呢?根据其结构特点我们可以看出：
一、so...that与too...to的转换
当that引导的从句为否定式时，从句主语与主语的主语相同时，so...that可转换为too...to结构;若从句主语与主句的主语不相同时，so...that可转换为too...for sb.to结构。例如：
He is so young that he can't go to school.→ He is too young to go to school.
The box is so heavy thathe can'tliftit.→The box is too heavy for him to lift.
二、so...that与enough to的转换
1.当that引导的从句为肯定式时，若从句主语与主句主语相同时，so...that可转换为 enough to结构;若从句主语与主句主语不相同时，so...that可转换为enough for sb.to结构。例如：
Tom is so old that he can go to school.→Tom is old enough to go to school.
The box is so light that the child can liftit.→The box is light enough for the child to lift.
2.当that引导的从句为否定式时，若从句主语与主句主语相同时，so...that可转换为enough to的否定结构;若从句主语与主句主语不相同时，so...that可转换为 enough for sb.to的否定结构。注意：转换后的形容词(副词)要用其相应的反义词。例如：
The man is so old that he can't go to work.→The man isn't young enough to go to work.
The desk is so heavy that I can't moveit.→The desk isn't light enough for me to move.
三、enough to的句式为否定式时，enough to可以转换为too...to结构。但转换后的too...to结构中的形容词(副词)要用其相应的反义词。例如：
He is not old enough to do the job.→He is too young to do the job.
Tom didn't walk slowly enough for us to keep up with him.→Tom walked too fast for us to keep up with him.