by many years 和 for many years区别

题目

by many years 和 for many years区别
总是有些题目把他俩拿来对比,总是搞错,郁闷阿,查字典也查不出来

答案

many years before 用于过去的过去（过去完成时）,有对比关系
many years ago 表过去（一般过去时）