結構是:How +形容詞+ a / an +單數的可數名詞 +主謂。如:
How good a boy it is
How +形容詞或副詞 也可以加(主語+謂語)
如:How beautiful the bird is!
而what+a/an+形同詞+可數名詞單數+主語+謂語
如:what a tall building it is!
what+形容詞+複數名詞或不可數名詞+主語+謂語
what clever students they are!
特殊的就是:表天氣的不可數名詞,前面加形容詞修飾時要加定冠詞,如:what a heavy rain