"how"和"what"都可以用来引导感叹句，它们的主要区别在于强调的成分不同。

How引导的感叹句

结构：How + 形容词/副词 + 主语 + 谓语

例子：

How hot it is today!

How well she sings!

How time flies!

How clever the girl is!

How fast the runner runs!

What引导的感叹句

结构：What + a/an + 形容词 + 可数名词单数 + 主语 + 谓语

例子：

What a good girl she is!

What an interesting book it is!

What beautiful flowers they are!

What kind women they are!

What nice music it is!

有时"how"和"what"可以互换使用，句意相同。例如：

How clever a girl she is! = What a clever girl she is!

How delicious these cakes are! = What delicious cakes these are!

此外，在口语中，为了强调起见，"how"或"what"引导的感叹句可以改为感叹词 + 谓语 + 主语。例如：

How impressive was the play!

What a fool is he!

总结：

How修饰形容词或副词，强调程度或方式。

What修饰名词，强调名词本身。