GMAT Sentence Correction (SC) | Re: Many of them chiseled from solid rock centuries ago, the

The source of this topic seems to be the condemned 1000 series. Notwithstanding that, let's see whether we can have any take away from that, especially because MGMAT is has been cited in the discussions on the principles of modification
Following is an excerpt from the Manhattan guide:

1. Right: This model explains all known subatomic particles, SOME OF WHICH WERE only recently discovered.--

The question is whether the second part of this sentence is an IC or just a modifier clause. IMO, \it
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