be used as \be used for\be used by 的区别

问题描述:

be used as \be used for\be used by 的区别

be used by,被.使用.如:
This knife is used by me.
be used for,被用来做什么事情.如:
This knife is used for cutting fruit.
be used as,被用来做什么东西.如:
This knife is used as a tool.