【Prep】一道it指代问题

杀G曼巴

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
  
  
  
  
  OA 没疑问，就想讨论一下关于E ：
  
  
  Ozone, a special form of oxygen that screens out harmful ultraviolet rays, reaches high concentrations twelve miles above Earth, where it had long appeared that it was immune to human influence; we have now realized, though, that emissions of industrial chlorofluorocarbons deplete the ozone layer.
  
  
  这里第二个it指代的是Ozone，第一个it在这里算什么用法？这两个it在这里感觉很奇怪，但具体怎么个奇怪法，求指导
  
  
  
  
  
  
  

杀G曼巴

那个OA后面的 D  怎么自动变成一个笑脸了......

杀G曼巴

正确选项的it 指代Ozone没问题。

我觉得E的第一个it 的意味大概是 it appears that it 这种，有点形式主语那种感觉。应该不优，但我还没有很solid 的 evidence。有NN来指点一下吗。

所以 DE这里it区别其实很大