To my dear instructors, Stacey and Ron, I am having an issue understanding the usage of the term "extending". I have come across three similar questions that test this concept, and my comprehension is still lacking.

One example comes from the OG, so I will not be posting it. The other two examples come from the Quest for 750: Sentence Correction Slam Homework Bank.

Question 8:
Vietnamese researchers have recently conducted the first comprehensive study of what could be the most expansive architectural structure found in northern Vietnam, a labyrinth of narrow tunnels constructed around 400 B.C. and extends for more than 25 miles underground.

The explanation of why "extends" should be "extending" from MGMAT is as follows: This answer choice supplies the appropriate modifier “extending” that is idiomatic and structurally parallel to the previously mentioned modifier “constructed.” Both modifiers refer to the “labyrinth of narrow tunnels” and thus must be structurally and logically consistent. (Note: To my surprise, the OG guide's explanation does a slightly better job at explaining this, but again, I cannot post it, and even if I could, it still goes over my head).

1. First, how is "extending" parallel to "constructed"?
Wouldn't it be "extended" that is parallel to "constructed"?
Why would "extended" be incorrect in this context?


2. Second, this clause makes sense to me:
...a labyrinth of narrow tunnels constructed around 400 B.C.

However, this clause sounds completely awkward:
...a labyrinth of narrow tunnels extending for more than 25 miles underground.

Wouldn't it have to be
...a labyrinth of narrow tunnels [that is] extending for more than 25 miles underground.
or
...a labyrinth of narrow [tunnels'] extending for more than 25 miles underground.


Question 29:
Egyptian geologists have recently discovered what could be the largest pre-historic irrigation system found to date, a sophisticated structure of interwoven pipes created more than 5,000 years ago and extending for more than 12 miles from the Nile delta.

The issue with "extending" and "created" here is analogous to "extending" and "constructed" above.


I would love a detailed explanation about this term "extending". Thanks!

This is a slightly weird issue.

First, you mentioned that "a labyrinth of narrow tunnels constructed around 400 B.C." sounds fine to you but "a labyrinth of narrow tunnels extending for more than 25 miles underground" does not. This is where we don't just want to rely on our ears. I think they both sound fine. You don't. How can we possibly reconcile that just based on what they sound like? :)

Does this sound any better? the room contained a maze of cubicles extending the entire length of the room. If so, the construction is essentially the same as that in the labyrinth question. "extending" just means stretching that far, going along for that length - that sort of thing. If not, oh well - read on.

For the labyrinth question, the second part of that offers to modifiers describing something about the labyrinth, yes?
1) constructed around...
2) extending for...

So, I do want both of these in modifier form, consisting of the participle form of a verb. Past participles are constructed with -ed endings for regular verbs (there are many irregular ones, of course) and present participles are constructed with -ing endings.

Is the construction still occurring today or is it entirely in the past? It was in the past, so I use the past participle constructed.

Is the labyrinth still "extended" today - that is, is it still stretching out for that length today - or was that only so in the past? They just did the study, so the labyrinth is still extending today - use the present participle extending.

These are parallel because I'm using the participle form for both - the unusual thing here is just that the two modifiers apply to different time frames, so I have to adjust the wording accordingly.

I don't want to use "extends" because that is a conjugated form of the verb (present tense) - so that's definitely not parallel to the participle form. I also don't want to use "extended" because the labyrinth is still extending - it still exists, according to the original sentence. If I used "extended" I would mean that it no longer does.

How's that - does that help?