Sentence Correction (SC) | The growth of the railroads led to the abolition of local times, which

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Yes, the two elements could be considered parallel. So, there's not, strictly speaking an issue with parallism.

The issue is with the tense of "were differing."

To see this issue more clearly, consider this version of the (C) version of thesentence.

The growth of the railroads led to the abolition of local times, which were ...differing from city to city, and to the establishment of regionaltimes.

We see that the sentence illogically uses the past continuous
...

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