SC OG12-95求助

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 the air
that forms them is moving rapidly, are
(E) stationary crests and troughs although they are
formed by rapidly moving air, is
Agreement
Th e subject of the second independent clause is
the resulting fl ow pattern; this singular subject
requires the singular verb is known, not the plural
verb are known. While the long descriptive
construction between the subject and verb may
make it diffi cult to see this relationship, notice
that the modifying phrase is set off with commas.
Th e use of the active voice in the verbs of the
subordinate clauses provides greater clarity of
meaning.
A Plural verb does not agree with the singular
subject.
B Plural verb does not agree with the singular
subject; the subordinate clause in the passive
voice following although is awkward and
unclear.
C Correct. In this sentence, the singular verb
is known agrees with the subject the resulting
fl ow pattern.
D Plural verb does not agree with the singular
subject.
E Th e subordinate clause in the passive voice
following although is awkward and unclear.
Th e correct answer is C.

虽然这道题目我选对了，但是我想问一下NN们，为什么这里B，E当中的passive voice不对呢？我没觉得它有什么awkward啊