Sentence Correction

I am unable to comprehend the explaination given by OG. Please kindly explain me & give me some tips to tacke these kind of questions. ANY HELP or detailed explaination would be really appreciated. Disclaimer. I am average student and have been really impressesed by many of you out there. So please do respond in detail.
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Question:
OG 10 685-206
The peaks of mountain range, acting like rocks in a streambed, produce ripples in the air flowing over them; the resulting flow pattern, with crests and troughs that remain stationary although the air that forms them is moving rapidly, are known as "standing waves".
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C. crests and troughs that remain stationary although the air that forms them is moving rapidly, is

E. stationary crests and troughs although they are formed by rapidly moving air, is

EXPLAINATION in OG.

Choice E uses the correct verb form, is but it incorrectly introduces a dependent adverbial "although" clause int a prepositional phrase(with crests...)Such depended clauses can only occur in the predicates of full clauses. C correctly puts the although clause inside the predicate of the relative clause. (that....rapidly)

OG explanations (and some of their strategies) are garbage. Buy a used Kaplan book from half.com for 99 cents plus shipping, and if it doesn't help your score I'll paypal you the $4.

Here's what OG meant:

'that...' is used to describe something inline --> OG is the worst book *that* I have ever seen.

'although' can be thought of as something that joins 2 related and complete-on-their-own sentences (or, as OG properly calls them, 'full clauses') --> *Although* (OG is developed by GMAC),(Kaplan is in the business of preparing for tests, not creating them).

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While on the topic of 'that', also note that 'which' is often misused in place of 'that'.

'That' - is used inline, and restricts the scope of what is being described.
'Which' - is used in a phrase set apart from the sentence, and describes but does not alter the meaning.

Example:

I ate all of the hamburgers that were delicious - means I did not eat ALL of the hamburgers -- only the ones that were delicious.

I ate all of the hamburgers, which were delicious - means I ate ALL of them, and by the way they were yummy. Note how the comma sets apart the part with 'which'.

Thank you for your help. One quick clarification so I am sure that I got it right.

"'although' can be thought of as something that joins 2 related and complete-on-their-own sentences (or, as OG properly calls them, 'full clauses')"

What made choice C 2 complete sentences\clauses?

My apologies, saabidi. I noticed the difference in the first word that followed crests and troughs, but neglected to discuss the 'although' that follows in choice C.

This whole thing is a mess. Try looking up relative clauses on Wikipedia and then imagine how you would list rules to teach a computer how to read English...

'Although' is principally a conjunction that is used in the manner I described before. However, if you think of it as merely a separator of two related but seemingly opposite ideas, the GMAT question might clear up.

As OG states, choice C puts the 'although' in the 'relative clause' (that...). Because of this, it is clear that the waves *remain stationary* although (read: despite the fact that) the air that forms them is moving rapidly.

In choice E, *although* a human can clearly see that we are contrasting the word 'stationary', the choice as written contains only a noun followed by the conjunction. It would be like saying 'Bob although they are formed by rapidly moving air'.