关键看主语前是名词还是形容词.
形容词是HOW ,名词是WHAT.
what+a\an+形容词＋名词＋主语＋谓语＋!
what a nice day it is!
如果是复数名词,a\an 就不加了
what nice people they are!
当然,主语＋谓语是可以省略的.
how＋形容词\副词＋主语＋谓语＋!
how nice the day is!
how fast the car rrns