prep1-75

75.   (28597-!-item-!-188;#058&003702)

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

答案：D

为什么答案中has become前不要逗号呢？a fungus that has for centuries slowly woven its way through the roots of trees and  不是作为插入语吗