请教大全987第4题 ?

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

请NN解释一下D为什么不对吗?

I will try to answer it.  I picked the right answer when I did that.  

First, although is ususually used to start a sentence, not in the middle.

Second, spots 'on' something, not spots 'at'  ie.  I see spots on your shirt, not I see spots at your shirt.  

Third.  'having' is a on going action, but it has not been sighted yet, therefore, it can't be an on going action.  'Although never have been sighted' would be better.  

OG解释

D Although usually introduces a subordinate clause, but there is no subject of the clause and having been sighted is not a complete verb phrase.

谢谢解释!

这是OG上的题吗?

11th OG 9

再问一下, 这道题的答案在OG11上是C还是A啊?

请好心人把OG11上的解释写一下.

谢谢!!!!