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.”

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

E为什么不对呢，看这也可以阿

忘记贴正确答案了，答案是c

E里面with stationary crests and troughs 是一个短语，although they are

formed by rapidly moving air是一个分句，怎么能有这种结构呢？although引导

的这个从句好歹也得要个主句吧！