be adj enough to v用法解析及句型转换
动词“be + 形容词 + enough + 动词不定式”结构是初中英语中最常用的句型之一，也是中考考点之一。同学们在学习和使用这个句型时，必须注意这个句型的主语是人还是物，是肯定结构还是否定结构以及与其它句型的相互转换。
一、句型结构
动词“be + 形容词 + enough + 动词不定式”结构的意思是“有足够的……做某事、到了做某事的……了”。句子的主语通常指人。例如：
1. Andy is generous enough to buy nice presents for all of us. 安迪够大方的了，给我们大家买了漂亮的礼物。
2. The boy is old enough to go to school. 这个男孩到上学的年龄了。
如果句子的主语指物时，必须在动词不定式之前加“介词for + 名/代词”作为动词不定式的逻辑主语。例如：
1. The question is easy enough for him to answer. 问题够简单的了，他能回答上来。
2. The box is light enough for her to carry. 这个箱子很轻，她能搬动。
该句型的否定结构是在动词be的后面加not，意思是“太……而不……”。例如：
1. The little girl isn’t old enough to go to school. 那个小女孩没有到上学的年龄。
2. The problem isn’t easy enough for him to work out. 问题太难了，他算不出来。
二、句型转换
A、与too…to…结构转换时，必须具备以下条件：
（a)“be + 形容词 + enough + 动词不定式”必须是否定结构。（b) “too…to…”结构必须用与前者相反的形容词。例如：
1. The little girl isn’t old enough to go to school.
The little girl is too young to go to school.
2. The problem isn’t easy enough for him to work out.
The problem is too difficult for him to work out.
B、与“it（形式主语）+ be +adj. + of +sb.+ 动词不定式(真正主语)”结构的互换。例如：
Sandy is generous enough to buy all of us nice presents.
It is generous of Sandy to buy all of us nice presents.
有时动词“be + 形容词 + enough + 动词不定式”结构与“so…that …”结构也可以互相转换，但这两种句型转换时，必须注意以下两点：
（a) 如果前者的主语指物，转换成 “so…that…”结构时，“so…that…”从句中必须用代词代替这个指物的名词。（b) 如果两种句型都是否定结构的话，“so…that…”结构中so后面的形容词必须用与前者相反的形容词。例如：
1. The boy is old enough to go to school.
The boy is so old that he can go to school.
2. The problem isn’t easy enough for him to work out.
The problem is so difficult that he can’t work it out.
温馨提醒：
“so…that…”结构可以与“such…that…”结构互换，但是“such…that…”结构不能与动词“be + adj.+ enough to do sth.”结构互换。
[中考实战演练]写出同义句（每空一词）
1. The box is too heavy for him to carry.（重庆市）
The box isn’t ________ for him to carry.
2. The boy is so young that he can’t swim across the river.（贵州省）
The boy _____ old _____ to swim across the river.
3. He is so strong that he can lift the heavy box.（河北省）
He is ________ to lift the heavy box.
4. Jack is too young to dress himself. （山东省）
Jack is not ________ to dress himself.
5. The boy is so young that he can’t look after himself.（广东省）
The boy is not ________ to look after himself.
Keys:
1. light enough 2.isn’t, enough 3. strong enough 4. old enough 5. old enough