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本贴相关题目 OG-2017-SC-687OG-2017-SC-687
OG-2016-SC-19
OG-2015-SC-17
OG-13-SC-17
OG-12-SC-14
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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.

Aare visible as dark spots on the surface of the Sun but have never been sighted on
Bare visible as dark spots that never have been sighted on the surface of the Sun
Cappear on the surface of the Sun as dark spots although never sighted at
Dappear as dark spots on the surface of the Sun, although never having been sighted at
Eappear as dark spots on the Sun's surface, which have never been sighted on