Doubt -- 2 options

[anshulagarwal12]

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, is

(B) stationary crests and troughs although they are formed by rapidly moving air, is

[GMATGuruNY]

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, is

(B) stationary crests and troughs although they are formed by rapidly moving air, is

I offered an explanation here:

https://www.beatthegmat.com/peaks-of-a-m ... 78057.html

[CSASHISHPANDAY]

I go with option crests and troughs that remain staitionary altough the air that forms them is moving rapidly, is


Reason parallelism between the 2 principal parts (crests...stationary and air...rapidly)