Great explanation by Erin -- had to share

[flex_manny]

These are the kind of explanations we need. Helps clear some doubts about usage of parallel
The growth of the railroads led to the abolition of local times, which was determined by when the sun reached the observer’s meridian and differing from city to city, and to the establishment of regional times.

(A) which was determined by when the sun reached the observer’s meridian and differing
(B) which was determined by when the sun reached the observer’s meridian and which differed
(C) which were determined by when the sun reached the observer’s meridian and differing
(D) determined by when the sun reached the observer’s meridian and differed
(E) determined by when the sun reached the observer’s meridian and differing

Make sure you read the second PART
Explanation by Erin
Part 1
A couple of important grammar points here. Let's start with the "original" (without ellipsis (GMAT Sentence Correction: The growth of the railroads led to the abolition...), reduction, etc.) sentence:

The growth of the railroads led to the abolition of local times, which were determined by when the sun reached the observer’s meridian and which differed from city to city, and [the growth [of the railroads [also] led] to the establishment of regional times.

This is what the "original" sentence would look like. You will notice that:

which were determined

is parallel with

which differed

These two parts are adjective clauses and can be "reduced" such that they become adjective phrases (or participial phrases in this particular case):

determined

is still parallel with

differing

Okay, that's the first point.

The second point is this:

The growth of the railroads led to the abolition of local times, which was ==> were determined by when the sun reached the observer’s meridian and differing from city to city, and to the establishment of regional times.

because "were" is the verb for the relative pronoun "which," which replaces the head noun "times."

And I think these two rules should give you answer choice (E).

Part !!! --differed versus Differing

It's a bit tricky to answer these questions sometimes, but the main idea behind whether to choose the -ing form or the -ed form this:

When we reduce a verb to its -ing or -ed form, we must look at one and only one thing: whether the noun that it will modify is the subject or object of that verb.

The -ing form is used for DOING the action, which means SUBJECT, which means ACTIVE voice.

The -ed form is used for RECEIVING the action, which means OBJECT, which means PASSIVE voice.

Before I go further, let me offer two examples that will make things clearer as we go along:

• speaking person (the -ing form)
• spoken words (the -ed form)

In this type of question, we always have two elements:

• a particple, which is either in the -ing or -ed form
• a noun that is modified by this participle

So, using the previous examples, speaking modifies person and spoken modifies words.

The next step is to realize that these participles all come from verbs--speaking and spoken both come from the verb speak.

Now, using these examples, and applying them to the rules I mentioned at the beginning, we will notice that if we made a sentence, person would be the subject of the verb speak and words would be the object of the verb speak. Using this procedure, we can figure out whether should use the -ing or -ed form of a participle that modifies a noun. And that's it!!

Of course, this is easy when the vocab is easy, and we often get confused when we are using difficult vocab because we sometimes don't know whether something is the subject or the object of the verb, but this procedure that I have explained is the only sure way to get the right answer.

In our sentence here, which replaces times, and times is the object of determined, but it is the subject of differed.

In other words, we have something like this:

...somebody determined times...

but

times differed...

I know some of you have learned that we should only use the -ing form only for actions that are ongoing/in progress in the present, but that's simply not true. We do occasionally use them correctly for past actions that were ongoing/in progress.

Finally, everybody gets confused simply because the -ed form appears in the second one, making people think the -ed form should appear again when it's reduced. We need to realize that there is truly no connection (for our purposes here in GMATland, anyway !!!!) between the two; it's pure coincidence that each has the -ed form in it!!!

If you stick to the rules that I just wrote, you'll be okay.

[hina_0611]

In this que, my logic was going the same. But Erin is all the time the best. Thanks flex.

[kulfi]

Got it now!

[TaTum]

Excellent. Thank you for great explanation.