A ist better than B because it doesn't omit the "of", which is necessary to keep the sentence parallel.
I thought of that but when you put 'of' after 'and' to keep it parallel, the meaning is weired.
"black hole lies at the center of many of the 100 billion other galaxies estimated to exist in the universe
This sounds a bit awkard!
Where as in 'B', if you omit 'of' after 'and' the sentence clause becomes part of the theory
...so sounds better!
Yes it sound better, and I'm not absolutely in favour of A, but consider:
the black hole lies in the center of the Milky Way and of many of...
first, we agree of makes it parallel
second, I think: The black hole lies in the center of what
? Of the universe, of the Milky way etc. You need the "of" to define the location.
I'm German, so I'm already pretty averse against sentences like "society of pupils of the High school" ( bad example, but it should demonstrate a ugly and bumpy sentence), in German I'would say it in one term. Still I choose A.
Normally solely "and" is absolutely fine, but in GMAT I suppose it isn't.