Hey saw this question and perhaps I can put it in layman terms for you, as you still seem kind of confused. One thing I have noticed, whether it be with the GMAT experts here or professionals in the workplace is sometimes people get so good at what they are doing they know the technicalities of the, in this case test question, but have a hard time really dumbing it down for people who have no idea what the heck is going on. Not trying to step on all the experts toes here, but for me I learn really well if I can explain things I know to other people, and lord knows I need all the help I can get. But anyways, It took me about 15 seconds to figure out this question and here is my mental process, I hope it helps:
Immediately you can see BCD are ridiculous answer choices. If you understand like vs. As you can cross off B and C, and D doesn't make any sense. So you are left with A and E.
The Parthenon was a church from 1204 until 1456, when Athens was taken by General Mohammed the Conqueror, the Turkish sultan, who established a mosque in the building and used the Acropolis as a fortress.
(A) who established a mosque in the building and used the Acropolis as
(E) establishing a mosque in the building and using the Acropolis as
Well I mentally remove the turkish sultan because it isn't important and just get's in the way with trying to figure out the answer. So mentally, I read it as the conquerer who established a mosque in the building and used the acropolis as a fortress. Is this ambiguous in any way? I don't think so. The addition of who directly refers to this conquerer bro. You clearly know who established the mosque and used the Acropolis as a forest. It is definitive. I can't find anything wrong with A that would make it incorrect. That is a good start
Now you look at E and again I just read the sentence as: Athens was taken by General mohammid establishing a mosque in the building and using the Acropolis as.
I mean when you read it like that, one big fluid sentence, it sounds really weird and you can't really tell whether it is meant to be referring to The conquerer guy or the entire sentence. Even if you aren't sure what exactly is wrong with this, as in fact the test doesn't make you tell on every question what is wrong with it, you should know A is more definitively correct than E and less ambiguous.
My dumbed down explanation for the next question:
In the past several years, astronomers have detected more than 80 massive planets, most of them at least as large as Jupiter, circling other stars.
So what is most of them at least as large as jupiter referring to. PLANETS right? I mean obviously the astronomers aren't being compared in how large they are to Jupiter. What do the planets do in this sentence? They circle other stars right? I mean if you took out both the modifiers the sentence would read: Astronomers have detected more than 80 massive planets circling other stars. That is a complete sentence and makes perfect sense. The planets are circling other stars!
I hope my explanation helps. Perhaps it is not the most technical way to put it, but for some reason I have always been good at taking complex ideas and humorously breaking them down into easy to understand/ grasp ideas. Thanks for your time

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