[讨论]PREP SC 169-75

怎么也没找到PREP SC 169道题目的那套中,第75条的讨论,所以请大NN们帮忙看一看:

Beneath the soil of the Malheur National Forest in eastern Oregon, a fungus has for centuries been slowly weaving its way through the roots of trees, to become the largest living single organism known to humans.

(A) has for centuries been slowly weaving its way through the roots of trees, to become

(B) has slowly woven its way through the roots of trees for centuries, and so becoming

(C) that has been slowly weaving its way through the roots of trees for centuries has become

(D) that has for centuries slowly woven its way through the roots of trees and has become

(E) that, having slowly woven its way through the roots of trees for centuries, to become

这里C的has been weaving,我不理解为什么要用完成进行时?

谢谢!