OG12 SC95

ylj3618

95. 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
E. stationary crests and troughs although they are formed by rapidly moving air, is

为什么OG上说B里：the subordinate clause in the passive voice following “althouth ” is awkward and unclear?请NN们指教

mongmong

http://forum.chasedream.com/GMAT_SC/thread-575381-2-1.html

mongmong

ding

anguslu24

不明白og的扯淡，但是B中用了are就错了