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
OG说B 没有标点符合，On the surface 。。。of the sun是ungrammatical and makes no sense ；
什么意思？？？ | 
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发表于 2012-9-4 23:17:32
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