OG11 9再问指代问题，请指教

前几天，看了以前NN们的直待讨论，似乎觉得明了了不少。今天又看OG的时候发现了一个问题，望大家指点下我吧~谢谢！

OG 11-9

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.

答案是A，原句正确。

(E)appear as dark spots on the Sun's surface, which have never been sighted on    (E错在哪里呢？)

OG对E 的解释是The relative pronoun which should immediately follow its referent; here which illogically follows surface, and its intended referent, either sunspots or dark
  spots, becomes unclear.

这里OG认为which是就近指代的，可是OG上的很多题目中which并不是就近指代的啊。

比方说：Executives and federal officials say that the use of crack and cocaine is growing rapidly among workers, significantly compounding the effects of drug and alcohol abuse, which already cost business of more than $100 billion a year.这里的which不是指代effects吗？那不就是指代中心词了吗？

有点糊涂了.望NN们指教...先谢谢大家拉^-^

可是，我之前看的帖子讨论说，

代词的指代问题，有时是跳跃的，有时是就近的，具体地不仅要根据语法来看，还要根据逻辑来分析的啊..但OG这里说which是就近的，是不是矛盾呢？

不好意思啊..我还是有点糊涂..

你的意思是不是说which 可以做引导词，也可以做代词？

那么Executives and federal officials say that the use of crack and cocaine is growing rapidly among workers, significantly compounding the effects of drug and alcohol abuse, which already cost business of more than $100 billion a year.这句话中，which是不是做引导词引非限制性定语从句呢？那我可不可以把which看做是代词呢？

我不太明白按照你的说法，如何来区分which的是引导词还是代词呢？

啊，我明白了~

原来我一直错误地理解了which的作用啊...太感谢拉~

3Q，对which有点明白了