pranavsingh2911
GMATNinja egmat Why is A wrong, considering it has no idiom issues. Only has one extra word 'their'.
Consider how "their" impacts the meaning. Imagine you saw the following start to a sentence:
"The kids traveled to Maine without their...."
Your expectation is that whatever follows "their" is going to be noun that the kids possess right? They traveled without their dog. They traveled without their toothbrushes. Or something like that.
Now go back to (A). When I see "mood swings, which may be violent without their..." I'm expecting a noun possessed by the mood swings. But "their being," doesn't make any sense. They're violent with their essence? Nah.
If you read it over a few times, can you figure out that the writer isn't using "being" as a noun, but rather as a modifier? Maybe. But notice that (C) is more logical because it removes "their." Now there's no longer an expectation to see a noun possessed by the mood swings. Instead, it's clear that "being grounded" is a modifying phrase describing the "mood swings."
If one option is clearer and more logical than another, it's better. Simple as that.
I hope that clears things up!