GMAT Sentence Correction (SC) | Parallelism subtlety that is sort of important

I'd like to walk you through a question I have, and my initial conclusion. Let me know if the analysis or the conclusions are not sound:
Take a look at the Manhattan GMAT advanced section on parallelism to read about the background to this topic.
I think this is worth explaining on this forum because wordy and long sentence correction problems SUCK. These questions kill yourtime.

Question
Simple and Complex Gerund Phrases look very similar but you need to easily spot the differences between them
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