分类：教育/科学-外语学习-英语考试
问题：“一……就……”的用法？老师讲的是：ondoing和atdoin 
  讲的是：on doing和at doing但是强调了on 后面的doing是某些行为，at 后面的doing是视觉，听觉之类的动作，我没听懂。  有哪位高人来指点迷津吗？
回答：表示"一…就…"的结构 
  
　hardly/scarcely…when/before, no sooner…than　和as soon as都可以表示"一…就…"的意思，例：

　I had hardly / scarcely got home when it began to rain.
　I had no sooner got home than it began to rain.
　As soon as I got home, it began to rain.

　注意：如果hardly, scarcely 或no sooner置于句首，句子必须用倒装结构：
　Hardly / Scarcely had I got home when it began to rain.
　No sooner had I got home than it began to rain.