几个语法问题

tbs

细细的研究几个sc答案后，有几个模糊的地方想问清楚些，请大家帮忙，谢谢
新东方补充材料
262 Sunspots,vortices of gas associated with strong electro-magnetic 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C appear on the surface of the Sun as dark spots although never sighted at 我同意，但是是凭着感觉选的
D.appear as dark spots on the surface of the Sun , although never having been sighted at错在哪里？

351 In 1929 relatively small declines in the market ruined many (speculators having bought on margin;they had to sell ,and) their selling pushed other investors to the brink.
答案C speculators who had bought on margin;they had to sell,and
想知道A不好在哪里？不是分词由于从句吗？

359 A star will compress itself into a white dwarf, a neutron star, or a black hole after it passes through a red giant stage, depending on mass.全划线题
答案D Mass determines whether a star, after passing through the red giant stage, will compress itself into a white dwarf, a neutron star,or a black hole.
虽然我也选了它，但是疑惑这样一来句子的重心改变了吗？主语变了啊。

zyh79

1.D有一明显错误：having been sighted不简洁（ets最烦这种答案了）改为sighted
2。记住：名词后不能使用分词的完成使作定语。
   分词也不完全优于从句。
3。句子重心改变原则并不是说原句的重心就一定对，以句意需要为准。

primefang

对于3， 原句 的it 是明显的指代不清
                depending on mass, 分词在句末，表示结果，这里读来不通阿

cathy_zeng

2.从句与分词修饰的差别之一时当主从时态不一致时，不能用分词。