GMAT Sentence Correction (SC) | At the annual stockholders meeting, investors heard a

First, "among them" is NOT connecting an independent clause - there is NO clause after " among them", just two things: X (the threat) and Y (the decline) - without any verb.

"Among them X and Y" is a (special) noun modifier referring to "challenges".

One way to remember this construction is to identify the similarity of its structure with a subgroup modifier's
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