I'll jump in and say that this question is one that we use in our parallelism lesson to demonstrate how lists of things need to be similar in nature. Only the correct answer to #119 has a gerund, but more importantly, only that answer choice fits in with the other items in the list- reversals (a thing), the onset (a thing).
Like Tim, I'd say it's great for you to learn these things and is helpful to understand and better use the English language, but knowing the differences between complex grammatical terms is not something the GMAT requires. If it did, almost everyone would be in trouble!