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题库 / Prep2007E2-SC-8
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.
has long appeared that it was immune from
has long appeared to have been immune from
has long appeared as being immune to
had long appeared immune to
had long appeared that it was immune to
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2.在we have now realized已经是现在完成，意味着在过去某个时间点之前我们都以为ozone是 immune from human influence，自然应该用过去完成时态。
3. it appeared后面加从句it blah blah是redundant，appear作为系动词，后面可以直接加形容词做表语。这样最为简洁清楚。
Have/has = present perfect (started in the past and continues until now)
Had = past perfect (happened before another event in the past)
1. You need a past tense in order to use the past perfect (I had studied for three years before I took my GMAT).
2. The usage of past and present perfect tenses could work, but again, you need a simple past to say when something started in the past (I had studied for three years before I took my GMAT, but since then I have not wanted to study).
3. The biggest error in the sentence (I have received a high score in GMAT because I had prepared hard for it" is wrong) is meaning: receiving a high score is a one time event (past) not a continuing event (present perfect).
as being immune to 这种说法太wordy了，GMAT要求语言简练，直接排除C；类似的题目还有很多；
剩下DE；
seem，appear，look，feel，smell，sound，taste是系动词，后面可以直接跟形容词；D很简洁又正确；
E is too wordy. "appeared immune" is just fine on its own. Notice that we have "it appeared immune." The "it" here refers to the ozone. Thus, to say: "it appeared that it was immune" would be unnecessary.
seem, appear, look，feel, smell, sound, taste是系动词，可以替换成be动词，直接接形容词
E 第一个it形式主语，第二it臭氧，代指不同错误
C 时态不正确，时态应该比have now realized早"
ron：the past time is implied in the context -- it's whenever we made the discovery that human activities can affect the ozone layer.
immute to... 不受...影响; immune from... 免除...
seem, appear, look，feel, smell, sound, taste是系动词，可以替换成be动词，直接接形容词
appear 表现得，类似于be， 后面加表语，那么AE就不对
BC的been与appear是重复的，所以不对
It appears that there has been a mistake. 看来有一个差错。
It appears unlikely that interest rates will fall further. 看来利率不大会再降低。
The ozone had appeared immune, but now we have realized……。had表示在我们意识到某事之前，人们不是这么看它的。
seem, appear, look，feel, smell, sound, taste是系动词，可以替换成be动词，直接接形容词；同时，系动词没有被动式，不管人还是物发起都用主动式，如：it tastes good; it appears nice.
immune from... 免除...
"immune from" means free of exempt from (eg. immune from prosecution), whereas "immune to" means not susceptible (eg. immune to chicken pox).
2.在we have now realized已经是现在完成，意味着在过去某个时间点之前我们都以为ozone是 immune from human influence，自然应该用过去完成时态。
3. it appeared后面加从句it blah blah是redundant，appear作为系动词，后面可以直接加形容词做表语。这样最为简洁清楚。
2 在we have now realized已经是现在完成，意味着在过去某个时间点之前我们都以为ozone是 immune from human influence，自然应该用过去完成时态。
3. it appeared后面加从句it blah blah是redundant，appear作为系动词，后面可以直接加形容词做表语。这样最为简洁清楚。
语意，D更优