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 onthe Sun’s poles or equater.
划掉的部分是插入语，所以主语是sunspots
(A) are visible as dark spots on the surface of the Sun but have never been sighted on==>这是svo but vo的结构，时态没有问题，but have never...的逻辑主语也没有问题，语法和句义都符合
(B) are visible as dark spots that never have been sighted on the surface of the Sun ==>这个选项的意思和A有很大的差别，要分清楚原句的意思是sunspots have never been sighted on the ....还是dark spots have never been sighted....，因为这个that就近修饰的是spots, 而这里的dark spots是用来作比较参考的东西，所以根据句义这个选项的修饰对象有问题
(C) appear on the surface of the Sun as dark spots although never sighted at ==> 这个选项的句义改的就更加离谱了，sunspots是作为dark spots appear on the surface of sun, although 后的逻辑主语是sunspots, never sighted at
(D) appear as dark spots on the surface of the Sun, although never having been sighted at ==> 和C 一样的问题，而这个问题更加严重，haveing been 了，哪有现在在进行吗。在G的规则中，进行时都是少用的，别说是现在完成进行时了。manhann bible里说了，这种自然规律通常都是用一般现在时的，不用进行时的
(E) appear as dark spots on the Sun's surface, which have never been sighted on==>which修饰有问题，后面的内容都是修饰surface的， 可以看得出来逻辑句义已经错误了
中文分析的很奇怪的，但是gmatclub有关于这道题的分析，他们说的很清楚
Option-C,D: are out since the sentence is not a cause-effect sentence i.e Reason for sunspots being visible on the surface of the sun, is not because they are never sighted on the Poles or equator.
Option B: modifies dark spots which changes the intended meaning
Option E: modifies surface and that makes no sense
Option A: Correct.
http://gmatclub.com/forum/sunspots-79261.html
fyi
其实最近复习manhann 的SC bibile以来就觉得，所谓的逻辑句义不对，就是修饰错误
-- by 会员 清飞扬 (2011/8/12 19:35:24)
这个我理解错了。