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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
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