为帮助大家有效备战2015年GMAT考试，新东方小编在此与各位分享OG13中Sentence Correction(句子改错)140题的详细解析，希望对备考有帮助。
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17. Sunspots, vortices of gas associated with strong electromagnetic activity, are visible as dark spots on the surface of the Sun but have never been sighted on the Sun’s poles or equator.
(A) are visible as dark spots on the surface of the Sun but have never been sighted on
(B) are visible as dark spots that never have been sighted on the surface of the Sun
(C) appear on the surface of the Sun as dark spots although never sighted at
(D) appear as dark spots on the surface of the Sun, although never having been sighted at
(E) appear as dark spots on the Sun’s surface, which have never been sighted on
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(A)are visible as dark spots on the surface of the Sun but have never been sighted on
【正确】 “are visible as dark spots on the surface of the Sun”和“have never been sighted on the Sun's poles or equator”用“but”平行在一起，语法上正确，表意也十分合理。
【大意】 太阳黑子，和强电磁活动相关的气旋，以黑点形式在太阳表面可见，但从未在太阳的两极或赤道被发现。
(B)are visible as dark spots that never have been sighted on the surface of the Sun
【错误】 平行结构：“are visible as dark spots”和“never have been sighted”逻辑含义上应当平行，共同描述“sunspots”的两种性质——“太阳黑子”以黑点形式在太阳表面出现，但从未在太阳两极和赤道被发现(即(A)的大意)。而本选项将这两者变为修饰关系，用“never have been sighted”修饰“dark spots”，则其大意为“太阳黑子以从未在两极或赤道出现的海淀在太阳表面出现”，逊于(A)选项的含义。
句子意思：“of the Sun”是一个赘余的结构，和其后的“the Sun's poles”完全无法衔接。
(C)appear on the surface of the Sun as dark spots although never sighted at
【错误】 句子意思：句子的结构含义不合理，“although”后面连接的应为让步的结构，其不会作为一个句意的中心，而根据日常逻辑，“太阳黑子从未在太阳两极或赤道被发现”是本句句意重心之一，因此(C)表意逊于(A)。
(D)appear as dark spots on the surface of the Sun, although never having been sighted at
【错误】 句子意思：见(C)。
(E)appear as dark spots on the Sun's surface, which have never been sighted on
【错误】 平行结构：类似地，见(B)。
【最优解题思路推荐】
当平行结构把应该平行的东西——语法功能一致，逻辑概念对等的结构排练在一起时，可以非常工整地反应一个事物的两个侧面或一句话的两方面内容，其表意具有优越性。因此选择(A)。
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