OG 10 : VR : 205 : The peaks of a mountain range ...

The peaks of a 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." 

(A) crests and troughs that remain stationary although the air that forms them is moving rapidly, are 
(B) crests and troughs that remain stationary although they are formed by rapidly moving air, are 
(C) crests and troughs that remain stationary although the air that forms them is moving rapidly, is 
(D) stationary crests and troughs although the air that forms them is moving rapidly, are 
(E) stationary crests and troughs although they are formed by rapidly moving air, is

For E,

....,[PP]with stationary crests and troughs [DC]although the air that forms them is moving rapidly, ....

OG> incorrectly introduces a dependent

adverbial although clause into a prepositional phrase

(with crests ...)

For C,

...,....,with [IC]crests and troughs that remain stationary [DC]although the air that forms them is moving rapidly,....

OG>correctly puts the although clause inside the predicate

of the relative clause (that... rapidly)