yeah i dunno i guess i didn't understand the meaning of the original sentence... the "and orbiting spacecraft" kept throwing me off because i was thinking that it needed to be "and an orbiting spacecraft"

Good question - I don't love B, but it doesn't have any definite GMAT errors, so it's a legitimate choice.

E is wrong because of the modifier "shrouded by clouds". Venus, the planet, is shrouded by clouds; its geology cannot be shrouded by clouds, as its geology is an attribute of it, but not a planet or feature itself.

Modifier errors like that should be fairly easy to spot - so often, they exist at the beginning of a sentence (like they do here), so train yourself to look for those. If you can eliminate an answer choice after only reading the first 6-7 words, you save a lot of time and energy!

I have trouble with the ones that are odd but don't have any errors... not a fan of those - or any SC for that matter haha

The key, Money, is to embrace that! It's a much more methodical way of approaching SC than is going by feel. My first read through this one, I didn't like any of them, but I immediately asked myself "which ones have fatal flaws?", and came up with:

A) ..."and whose" needs a parallel counterpart to use "and", and there isn't one. WRONG
B) I don't love it, but I can't pinpoint a true error
C) The modifier to start seems a little off...is Venus intermediate between Earth and Mars, or is its geology? And has its geology been mapped, or has the planet itself been mapped? The Modifier and the Accuracy of this one seem to both be in doubt.
D) The pronoun "its" at the end is unclear in its referent - is it "radar"? If so, that's illogical. Is it "Venus"? It seems like it should be, but that's unclear.
E) That modifier at the beginning of the sentence is incorrect.

I just wrote in another thread to some international students who lament that English grammar seems to be an arbitrary thing for business schools around the world to test - it's this methodology, however, that makes it not only fair, but also a pretty good test of problem solving. In tough questions, the right answer should sound a little awkward - that's what throws you off the scent. But in business, as well as in Sentence Correction, the right decision will typically come from analysis, and not just what "feels right". These questions determine how well you can perform that kind of process-based analysis, and if you embrace that, you should do well!

Thanks money and Brian for your replies. It makes so much sense now why E is wrong. I guess I just crossed off B because it didn't sound right to me. It's so hard sometimes to go by the grammar rules and stop listening to your ear. Also, I have to remember that the right answer doesn't mean it's the perfect answer

The geology of Venus can only be intermediate between the geology of Earth and the geology of Mars; hence, 'that of earth' and 'that of Mars'.