ago和before的用法区别

问题描述:

ago和before的用法区别
I came back three days ago与I came back three days before或I came back before three days之间的区别?
再问:“我回来已近三天了” 能用这三个句子表达吗?

习惯上的表达有以下两种:
I came back three days ago
I came back before three days
区别在于ago可以用在最后,一般before后面还有内容