It's+形容词＋for＋代词＋to＋动词
It's+形容词＋of＋代词＋to＋动词
这两种句式都是 ”做什么事情对某人来说怎么样“ 用for sb ,形容词是 difficult, easy, necessary ,important之类；用of sb 形容词是可以修饰某个人的,例如 nice,kind, clever, polite, clever 之类.
It's difficult for him to learn English well.
It's nice of you to help me.
主语+形容词＋enough＋to＋动词 是”某人/某物 足够.,可以做什么...“
He is old enough to go to school.
否定句可以和 too...to.转换 He isn't old enough to go to school= He is too young to go to school.