Sentence Correction (SC) | Re: The rapid-rail lines that were recently introduced in southern

The rapid-rail lines that were recently introduced in southern California have had positive effects:not only have they lowered pollution levels, they have helped in decongesting the region’s freeway system, which had been operating far above its capacity.

A.not only have they lowered pollution levels, they have helped in decongesting
B. the lines have not only lowered pollution levels, but also helped to decongest
C. not only have pollution levels been lowered, but they have helped to decongest
D.