张道真《英语语法大全》上册第 596 页：
She is enthusiastic to advise him. ×
She is enthusiastic enough to advise him.√
The dog is clever to understand you.×
The dog is clever enough to understand you.√
The road is long to reach your village.×
The road is long enough to reach your village.√
有点不太理解为什么张道真教授说 enthusiastic, clever, long 后需要加 enough，是从句意角度吗？搜了下 COCA，enthusiastic to 有 68 条，enthusiastic enough to 仅有 6 条。谢谢各位老师！
be enthusiastic to do sth. （正。趋向形容词与不定式搭配，表示情态意义“热心做某事”，类似ready, eager, anxious, curious to do 等使用方法）
be clever to do sth.（正。品质形容词与不定式搭配也非常容易见到，不定式动作是品质的具体体现。还可说：It is clever of sb. to do sth.）
be long to do sth.（误。度量形容词与不定式搭配，需加上程度副词 enough，让不定式作结果状语）
前两个搭配加上enough，也正确，但不是需要。加 enough 后，跟第三个一样，不定式变成结果状语。