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
that从句修饰crests and troughs 还是
troughs，还有句中的they，them该怎么看，不知道我表达清楚了没有。。。
og对e的解释是：the subordinate clause in the passive voice following although is awkward and unclear .
这里的unclear是指什么？是说they的指代不明确么-- by 会员 aannaa (2011/9/11 9:13:50)
我个人认为，从句是修饰crests and troughs整体的。they也因此指代这两者，因为and已经形成compound plural words了。