…enough to是英语中一个常用结构，它可与so…that，too…to在一定条件下相互转换，并经常成为中考命题的对象。那么在什么情况下三者可以相互转换呢？
　　Ⅰ. …enough to 和so…that的转换
　　①当that引导的从句为肯定式，且从句主语与主句主语相同时，so…that可转换为 …enough to结构；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：
　　She runs so fast that she can get there first.
　　=She runs fast enough to get there first.
　　The question is so easy that he can answer it.
　　=The question is easy enough for him to answer.
　　②当that引导的从句为否定式，且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；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。但要注意，转换后的形容词（副词）要用其相应的反义词。例如：
　　Mr. Black is so old that he can’t go to work.
　　=Mr. Black isn’t young enough to go to work.
　　The box is so heavy that I can’t move it.
　　=The box isn’t light enough for me to move.
　　Ⅱ. …enough to与too…to的转换
　　当…enough to结构为否定式时，…enough to可与too…to结构相互转换。但要注意，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：
　　The problem is too difficult for me to work out.
　　=The problem isn’t easy enough for me to work out.
　　Ⅲ. so…that与too…to的转换
　　当that引导的从句为否定式，且从句主语与主句主语相同时，so…that结构可转换为too…to结构；从句主语与主句主语不相同时，so…that可转换为too…for sb. to结构。例如：
　　She was so angry that she couldn’t speak.
　　=She was too angry to speak.
　　The ice is so thin that we can’t skate on it.
　　=The ice is too thin for us to skate on.