gmat practice test1-14 关于过去完成时的时间状语问题？

14.Less than 35 years after the release of American honeybees outside Sap Paulo, Brazil, their descendants, popularly known as killer bees, had migrated as far north as southern Texas.

A)      Less than 35 years after the release of American honeybees outside Sap Paulo, Brazil,

B)      In less than 35 years since releasing African honeybees outside Sap Paulo, Brazil,

C)      In less than 35 years since African honeybees had been outside Sap Paulo, Brazil,

我的解题思路：由于主语和谓语分别是：their descendants, ..... had migrated as far north as southern Texas.  had migrated 过去完成时，看上去 跟since的表达更为合适， 则在b,c中选， since releasing不是gmat prefered usage, 所以选了c, 而key是a, 不知我的问题出在哪里了。求助！

b和c和楼主所说的完成时态没关系吧，都是in xxx years。

我记得在 in xxx year(s)这种结构里，能用完成时态的只有 in last year

我觉得A的表达很清晰，在honeybee释放后不到35年，就已经XX。