------ ---- useful piece of advice the teacher gave us.为什么用what
问题描述：
------ ---- useful piece of advice the teacher gave us.为什么用what
请说明理由
答
应该是What an吧?
这句话是感叹句
How +adj.&adv.
What +n
What an useful piece of advice
修饰的是名词advice所以用What
而useful开头发音是元音所以用 an