Ozone, a special form of oxygen that screens out harmful ultraviolet rays, reaches high concentrations twelve miles above Earth, where it has long appeared to have been immune from human influence; we have now realized, though, that emissions of industrial chlorofluorocarbons deplete the ozone layer.
语法 Sentence Correction-3597
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正确的用户笔记
ian709 2014-06-17 23:56:15
B) appeared to have been immume中的现在完成时多余，因为前面has appeared已经表达了完成时态。
许栩 2016-11-12 15:54:26
has appeared 和 have been immune 时态表示多余
czyanling 2014-08-13 11:39:09
一般以为出现eariler的本句中要用had done的时态。但今天长见识了，如果后面出现了have done now/ have now done 强调have done的现在时态的话，那么前面的动作也自然要用had done过去完成时
siasiasia 2016-04-06 20:04:41
be immune to
fishanne 2016-02-10 13:00:23
appeared to have been immume中的现在完成时多余，因为前面has appeared已经表达了完成时态。
ypheroin 2016-01-29 20:13:40
has appeared to have been, 两个完成时，语义重复。
tina885386121 2016-01-28 09:33:26
完成时套完成时没有必要
fishanne 2016-01-15 16:12:56
have appeared 与have been immune 重复 immune from 豁免免除； immune to human influence 免受。。。影响；免疫
ypheroin 2016-01-13 15:21:54
to have been immune 这个不定式是做主语的（it是形式主语）不需要时态。
时光老人 2015-12-25 16:19:46
immune from 幸免于难
HYX 2015-11-19 13:58:06
to have been 的时态不对； appear to do 也不对
jhb999 2015-10-15 15:18:39
appeared to have been immume中的现在完成时多余，因为前面has appeared已经表达了完成时态
