prep 一道求教NN!

ddwantsmba

Ozone, a special form of oxygen that screens out harmful ultraviolet rays, reaches high concentrations twelve miles above Earth, where it has long appeared that it was immune from human influence；we have now realized, though, that emissions of industrial chlorofluorocarbons deplete the ozone layer.
(A) has long appeared that it was immune from
(B) has long appeared to have been immune from
(C) has long appeared as being immune to
(D) had long appeared immune to
(E) had long appeared that it was immune to
选D ,为什么用过去完成时？还有A的第一个it 到底指代哪一个？不是应该就近指代earth?为什么有人说指代ozone ?

susander

第二个句子用的现在完成时，表示已经认识到了，（过去，延续到现在）根据句子的逻辑意思appear是比realize还要早的一个动作，就是说比过去都要早，那么就要用过去完成时表示“过去的过去”

xiruihuang

it在分句里做主语，ozone在主句里做主句，it无论是从语法上还是逻辑上都是指代ozone的。
唔..好像这里没有就近指代这一说吧..

ddwantsmba

请问这个语法上的代词指代是怎么看的？

ddwantsmba

那么A的问题就是时态咯？两个it都指代ozone 吗？

xiruihuang

A的问题还有啊
appear只能是
appear to do
appear+adj.（appear是系动词）
没有appear that

还有
immune to习惯用语