4. 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（C）
(E) appear as dark spots on the Sun’s surface, which have never been sighted on
although 后不应该由be吗，成为完整的句子啊，为什么就深略了呢
看来半夜问题果然无人问津啊，拜托大虾答疑下，自己顶战个位子先
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