1.too+adj./adv. to+v.太...而不能做某事。

例：He is too young to go to school.

他年纪太小还不能上学。

2.adj./adv.+enough to +v.足够...而能做某事。

例：He is old enough to go to school.

他足够大了能上学了/他已到了上学的年龄了。

3.so +adj./adv.+that从句 如此...以致。

例：He is so old that he can go to school.

通常来说，这三种句型可用于同义句转换，具体如下：

too...to...

=not 反义词 enough to 。

=so...that 否定句。

例：He is too young to go to school.

= He is not old enough to go to school.

= He is so young that he can't go to school.