[求助]XDF-sec17-16

16.   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 he air that forms them is moving rapidly, are（C）

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

OG里解释although在C和E中不同，可我怎么看不出来啊？真急啊

又看了一下OG，我想OG的意思是E中although这个从句直接跟在with stationary crests and troughs 这个后面不妥，而C的话，用了一个定语从句，就没有了这个问题。

另外，C是主动，E是被动，主动优于被动。

拙见，忘大家指正。