4.     Lower-level management function most effectively when they have thorough training and unimpeded communication with workers, supervisors, and one another.

(A) management function most effectively when they have

(B) managers function most effectively when they have

(C) management functions most effectively when they have

(D) managers function most effectively when they have received（B）

(E) management functions most effectively when it has

答案是b，为什么d不行，多个received句意没有变多少吧？？

D没必要使用完成时

一般现在时足以