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.” (C) crests and troughs that remain stationary although the air that forms them is moving rapidly, is (E) stationary crests and troughs although they are formed by rapidly moving air, is 答案是C，我选E 但我看不懂OG的解释，有谁可以指点迷津吗？ 或是指出我选E的错误～ Choice E uses the correct verb form, is, but it incorrectly introduces a dependent adverbial although clause into a prepositional phrase (with crests...). In the textbook publishing business, the second quarter is historically weak, because revenues are (low and marketing expenses are high as companies prepare) for the coming school year. 此题原句即是正确答案。而我的疑问是，两个独立子句用连结词连结， 不是应该中间要加逗点吗？ 所以我觉得and前应该要加逗点 还是我的认知有错误？ 感谢解答～ --

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