fast本身就是副词形式。
fast可以是副词、动词名词，以及形容词。
扩展资料
How fast can you type?
你打字有多快？
Children grow up so fast these days.
如今孩子们长得真快。
There are no hard and fast rules about this.
这事没有什么硬性的规定。
Research indicates that eating habits are changing fast.
研究显示，饮食习惯正迅速改变。
Things are not moving as fast as we hoped.
事情的.进展不像我们希望的那么快。
