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Ozone, a special form of oxygen that screens out harmful

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TooLong150 wrote:
Very good question. ACE were awkward. I then had to use the "immune to" idiom to pick D over B. I did not understand how to split the answers using the tenses. Can someone explain how the past perfect is used correctly here?


Striking out prep. phrases and modifiers, we have..
Ozone, a special form of oxygen that screens out harmful ultraviolet rays, reaches high concentrations twelve miles above Earth, where it had long appeared immune to human influence; we have now realized, though, that emissions of industrial chlorofluorocarbons deplete the ozone layer.

Sequencing of the events is as follows.
Ozone appeared immune (1980s)---> scientists conducted some experiments (1990s) (say event X) ---> (1991) as a result of which we realize that cfcs deplete ozone layer.

'had (long) appeared' denotes that the action had happened in the past before an event X (imaginary event that also happened in the past)
'have (now) realized' denotes that the action is the result of event X (hence present perfect)

It is perfectly right to have a past perfect followed by a present prefect in a scenario such as..

Past perfect --> past action --> present perfect denoting the result of the past action)
Here past action is not necessary, because, present perfect is already denoting the result of the past action (implying that a past action had happened)
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New post 27 Jan 2014, 01:23
TooLong150 wrote:
Very good question. ACE were awkward. I then had to use the "immune to" idiom to pick D over B. I did not understand how to split the answers using the tenses. Can someone explain how the past perfect is used correctly here?


As a semicolon is here, we could see this whole sort of thing as TWO part. The second part(after the semicolon) told you that this is the situation NOW, "HAVE NOW REALIZED". Also, the context implied that the first part is the old view, and the second is a recent view. So it will be more reasonable to use a past perfect tense to make a comparison or just make it logically clear.

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TooLong150 wrote:
Very good question. ACE were awkward. I then had to use the "immune to" idiom to pick D over B. I did not understand how to split the answers using the tenses. Can someone explain how the past perfect is used correctly here?


There is some interesting conversations about the perfect tenses in this post :). You are starting off correctly with your question by looking at the split of tenses. The GMAT is providing you with a choice between the present and past perfect tenses. Generally speaking, the present perfect tense is used for actions that started in the past but they, or their effects, are still ongoing. The past perfect is used for actions that started in the past but have a definite end. The setup in this problem makes it very clear that the ozone "appearing to be immune" is something that is no longer happening, so you would eliminate the present perfect options.

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Re: Ozone, a special form of oxygen that screens out harmful [#permalink]

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New post 01 Dec 2014, 00:43
daagh wrote:
IMO, - immune from - is as acceptable as - immune to.-

E. g: Having suffered typhoid a couple of times, Tom is now immune to that disease.

You are immune from contracting sexually transmitted diseases, when you employ safe sex practices (meaning that you are protected from the ill effects of something, when you are immune from them.)

So what decides the use of - to or from - is the context. I would in the given context choose -immune from - rather than - immune to -because the meaning implies that ozone is far placed and hence protected from human influence.

What however baffles me is how we can afford a past perfect here, when the thumb rules state that

1. A past perfect can not remain alone without a simple past.

2. By custom, a past perfect can not be joined with a present tense or a present perfect, without a past tense intervening.

I can not digest choice D and E, unless somebody makes bold to say that the use of past perfect here is an exception under some blah, blah rule.

B on the other hand uses the present perfect tenses for all descriptions - has long appeared to - and -have been immune from - and it goes parallel with the present perfect in non-underlined part - we have now realized -

B for me therefore on my own reckoning.


I believe option D) is correct for many reasons that are mentioned above. Even the Past Perfect is justified here.

Please check for the comments posted above conveying the link between two independent clauses.

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Re: Ozone, a special form of oxygen that screens out harmful [#permalink]

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New post 21 Jan 2015, 02:59
TooLong150 wrote:
Very good question. ACE were awkward. I then had to use the "immune to" idiom to pick D over B. I did not understand how to split the answers using the tenses. Can someone explain how the past perfect is used correctly here?


Hey mate, I will try to address your doubt. If you read this piece of sentence " we have now realized, though, that emissions of industrial chlorofluorocarbons deplete the ozone layer." it is clear that scientists do not believe anymore that the Ozone layer is not contamined by humans. The use of present perfect, which underlines an action's continuation/perpetration/effect to present time is illogical. Using "had long appeared" you can efficiently convey the author's message. Between D and E you are obviously going to chose D, therefore you don't even need to consider the idiom issue discussed above.
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Re: Ozone, a special form of oxygen that screens out harmful [#permalink]

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I was between C and D.

I chose C, even though it sounds a bit awkward. The reason is that "had long appeared immune to" seems to be missing the verb "to be". So, I would have chosen D, if it was phrased as "had long appeared to be immune to".

One question I have is whether C is gramatically incorrect or not (C: has long appeared as being immune to).

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New post 27 Jan 2015, 20:33
No, "appeared as being" is not correct. Being is frequently used incorrectly (but not always!) so if you are between two options and you don't know how to eliminate, you can guess away from 'being'.
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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.

Meaning : Everybody thought that ozone was immune from human influence. But we have now realized that ozone is not immune.

a) has long appeared that it was immune from
As per the sentence, the action of appearing has ended as we have now realized that it is not immune. Hence the action of appearing cannot be present perfect. It has a definite end.

b) has long appeared to have been immune from
As per the sentence, the action of appearing has ended as we have now realized that it is not immune. Hence the action of appearing cannot be present perfect. It has a definite end.

c) has long appeared as being immune to
As per the sentence, the action of appearing has ended as we have now realized that it is not immune. Hence the action of appearing cannot be present perfect. It has a definite end.
And
being immune -> Action of immune is still continuing -> Which is absurd


d) had long appeared immune to

e) had long appeared that it was immune to
instead of "That it was immune" , we can use "immune" which means the same thing.

Doubts:
1) if there is a past perfect why not we have a simple past tense anywhere. We actually have.
Definition of present perfect is "The action happened in the past and either the action or its effect is still continuing when the statement is made".
We have now realized -> We started the process of realizing some time back but may be some experiments are still continuing or some investigation so the "effect" of realizing is not yet completed. Hence we have past tense of "action of realizing". A good question to practice indeed !!.
2) Immune to -> X is immune to Y -> X is already immune to something already.
Immune from -> X is immune from contracting Y (for example). So I guess we need another action if we use from.

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Ozone, a special form of oxygen that screens out harmful [#permalink]

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New post 30 Jun 2015, 06:37
tarek99 wrote:
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



Please explain your answer.

First of all, do "immune from" and immune to" exist in English or is it just one of them?

Thanks!


Past Perfect vs. Present Perfect. Before now, we thought that human cannot affect ozone; however, now, we have realized that ...
The former fact, our initial thought was true before now, so it does not include 'now'.
Present perfect can be used for a verb that happens or is true from past to now (including present)
From the above statements, it is clear that we cannot use peresent perfect here: Eliminate A, B, C

Placeholder 'it': the construction in E is much and unnecessarily wordier than that in D, it appeared that ...
I wouldn't say that choice is E grammatically wrong, but it is less preferable to D

in D: appear + adjective cinstruction is fine

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New post 14 Apr 2016, 08:27
tarek99 wrote:
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

Please explain your answer.

First of all, do "immune from" and immune to" exist in English or is it just one of them?

Thanks!



immune to or from is not a concern here...

If we notice we are talking about two events... 1) when the Ozone was immune and 2) when we realized that its not.
Tenses should reflect meaning.
A,B,C are out.
D - correct
E that it was is unnecessary and redundant (it had long appeared - already has it).

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Re: Ozone, a special form of oxygen that screens out harmful [#permalink]

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New post 17 Apr 2016, 06:29
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.

Meanining analysis (should be priority always) : IC 1 :ozone reaches high concetration levels at certain height, where it was immune from human influence - strong ozone!!
IC 2: now they've realized emissions deplete ozone - poor ozone!!
So ozone is no longer immune now, it appeared that it was (immune) earlier

a) has long appeared that it was immune from - has long appeared tells us that it appeared in past and still appears, but no this is not the case. out.

b) has long appeared to have been immune from - same error as above. out.

c) has long appeared as being immune to - same error as above. out.

d) had long appeared immune to - simple past tense would have sufficed as theres no other visible past tense verb for ozone for sequencing. rest all seeems ok anyways check next

e) had long appeared that it was immune to - why use that when I can simply say appeared immune to ..as in the above option so not a concise option. out.

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Re: Ozone, a special form of oxygen that screens out harmful [#permalink]

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New post 15 Apr 2017, 06:23
Hi Experts,

Could you please let me know what is the issue in option B apart from idiom?

has long appeared to have been immune from

here we are using perfect infinitive and it denotes the prior action then what is mentioned in main clause.

Please clarify this.

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Re: Ozone, a special form of oxygen that screens out harmful [#permalink]

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New post 15 Apr 2017, 15:15
PathFinder007 wrote:
Hi Experts,

Could you please let me know what is the issue in option B apart from idiom?

has long appeared to have been immune from

here we are using perfect infinitive and it denotes the prior action then what is mentioned in main clause.

Please clarify this.

Thanks


The use of perfect infinitive is wrong in this case - the fact that it is immune (or not immune) is an universal truth and use of perfect infinitive wrongly implies that it appeared that it was previously immune, but now it may not be.
Another problem with B is the wrong present perfect tense "has appeared". Since the verb "appeared" occured before the verb "realize", past perfect is better.

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Re: Ozone, a special form of oxygen that screens out harmful   [#permalink] 15 Apr 2017, 15:15

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