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题库 / OG12-SC-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".
crests and troughs that remain stationary although the air that forms them is moving rapidly, are
crests and troughs that remain stationary although they are formed by rapidly moving air, are
crests and troughs that remain stationary although the air that forms them is moving rapidly, is
stationary crests and troughs although the air that forms them is moving rapidly, are
stationary crests and troughs although they are formed by rapidly moving air, is
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求辨析C/E选项，谢谢
GMAC不喜欢被动句
although是从句，所以前面要有一个主句
stationary crests and troughs although they are formed by rapidly moving air，这里的although前面没有主句
crests and troughs that remain stationary although the air that forms them is moving rapidly，although前面that（crests and troughs ） remain stationary是主句
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