请教一道题目！！！

Dr.Tonegawa won the Noble Prize for discovering how the body can constantly change its genes to fashion a seeming unlimited number of antibodies,each specifically targeted at an invading microbe or foreign substance.

(A) seeming unlimited number of antibodies, each specifically targeted at

(B) seeming unlimited number of antibodies, each  targeted  specifically to

(C) seeming unlimited number of antibodies, all specifically targeted at

(D) seeming unlimited number of antibodies, all of them  targeted specifically to

(E) seeming unlimited number of antibodies, each targeted specifically  at

为什么选E，与A答案有什么区别，specifically位置改变有什么不同？请解释详细，谢谢！