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# Ozone, a special form of oxygen that screens out harmful ultraviolet r

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

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09 Jan 2017, 09:55
For those who may wonder why past perfect tense.

here's the fuller deal with the present perfect ("has/have VERBed"):
if you use the present perfect with a POINT EVENT - i.e., an event that OCCURS AT A SINGLE INSTANCE IN TIME (realized, graduated, paid, given birth, scored, etc.) - then the event must have taken place IN THE PAST.
normally this is the quite recent past, but that's not always the case.
my brother has obtained three business degrees.
the team has scored 32 points in this quarter.
Russia and the U.S. have sent expeditions to the moon.
these are all point events, and they are all PAST events.
the second is obviously in the very recent past, but the third is an event that happened over forty years ago (but to which we can still refer in the present perfect if it's relevant to the current topic of discussion). the first could be anywhere from a few minutes ago to 60-70 years ago, depending on my brother's age.

notice that, since these are "point" events, it's actually IMPOSSIBLE to refer to them in the present - unless you're narrating them, in the style of a sports announcer ("Demps scores a touchdown!")
so if you see them in the present perfect, they've already happened.

credit : RonPurewal
refer to : https://www.manhattanprep.com/gmat/foru ... t3584.html

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

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09 Jan 2017, 10:31
There are two primary issues here:

1) Idioms

"Considered," "Seemed," "appeared" are all words that are often unnecessarily proceeded by a preposition and an adjective. People say, "He seemed to be gigantic," or "She is considered as very industrious," or "they appeared to be insignificant." All of these examples are unnecessarily wordy. In each case the preposition shouldn't be there. "He seemed gigantic," "She is considered very industrious," and "they appeared insignificant" are all preferable to the versions with the prepositions. So when "considered," "seemed," or "appeared" is used to introduce a descriptive word (an adjective), don't use a preposition between the two words.

It's also idiomatic to say "immune to" rather than "immune from")

So D gets the idiom right.

2) Tense

As others have pointed out, D gets the sequence of events clear. The present perfect (which can be thought of as one version of the past tense, despite the name) in "have realized" tells us that the realization happened at some point before the present. We need to make clear that the old perception existed before that more recent realization. Past perfect (had appeared) makes this clear.

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

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09 Jan 2017, 11:53
udaymathapati wrote:
Ozone 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

What is the logic to answer? Is immune to idiomatically correct than immune from?

Something was appeared for Ozone, but now we HAVE realized something.

First event happened in past. Hence Present perfect is not required. A, B and C are out.

D) had long appeared immune to Concise and correct choice.

E) had long appeared that it was immune to 'that it was' is unnecessary and wordy.

Though I have got it correct. But I have a doubt with the source. We know that the past perfect tense is only used in the below two cases -
1. When two events happened in past and one happened before the other.
2. When a single event happened in past with a time clue somewhat after the event has occurred.

But neither of the scenarios happened here. Here, the sentence starts with a present tense and then jumped into a past perfect without a time clue is somewhat odd in gmat. Do you really think that that source is correct?

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

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10 Jan 2017, 03:42
arunavamunshi1988 wrote:
udaymathapati wrote:
Ozone 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

What is the logic to answer? Is immune to idiomatically correct than immune from?

Something was appeared for Ozone, but now we HAVE realized something.

First event happened in past. Hence Present perfect is not required. A, B and C are out.

D) had long appeared immune to Concise and correct choice.

E) had long appeared that it was immune to 'that it was' is unnecessary and wordy.

Though I have got it correct. But I have a doubt with the source. We know that the past perfect tense is only used in the below two cases -
1. When two events happened in past and one happened before the other.
2. When a single event happened in past with a time clue somewhat after the event has occurred.

But neither of the scenarios happened here. Here, the sentence starts with a present tense and then jumped into a past perfect without a time clue is somewhat odd in gmat. Do you really think that that source is correct?

I too consider that the use of past perfect is not justified - there has to be another verb in simple past or a time reference in order to use past perfect. Rather there is a time reference ("now") in present tense, and because of that reference, present perfect seems more appropriate than past perfect.

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

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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.

Thanks

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

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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.

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 ultraviolet r [#permalink]

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02 Sep 2017, 04:48
2 issues at play: Idioms and Verb Tense
-----------------------------------
IDIOMS
-----------------------------------
Split 1: Idiom "immune from" vs "immune to"
"X is immune to Y" is correct. A and B can be eliminated.

Split 2: Idiom "appear"
"Appear" has 3 uses that I know of: when followed by a verb, the verb should be in its infinitive form. examples:

(1) His arm appears to be completely healed
(2) She appears to have over \$2 million in debt (can you tell how cheerful I am tonight)

The 2nd use of appear: When appear is followed by an adjective, no transition is needed. examples:

(1) Karimi appeared unfazed by the threat of foreclosure. CORRECT
(2) Linda appears weak from the disease ravaging her intestines. CORRECT
(3) Frank appears that he is weak... INCORRECT

A ('Ozone has appeared that it was immune'), C ('Ozone has long appeared as being immune'), and E ('Ozone had long appeared that it was immune') can be eliminated.

-----------------------------------
VERB TENSE
-----------------------------------
First consider what we know to be right

"Ozone...reaches high concentrations..." The present is used because this is a constant through time (ie. 'eagles hunt baby birds')

"we have now realized..." The present perfect is used to express either (1) an action that started in the past but is still ongoing or (2) an action which began in the past but is relevant to the present context (ie. I have been to Paris' is better than 'I went to Paris' if we're talking about places we have visited). The present perfect "have realized" in this sentence indicates that at some point in the past, we realized something and that this realization is still relevant today (it's relevant to the current context because the sentence is talking about how that realization changed what we know about Ozone).

Tense split: Ozone "has appeared"/"had appeared" immune. Because the realization we made at some point in the past ('we have now realized') changed how Ozon appears, this underline verb should take up a tense that shows precedence to a past action. The past perfect "had appeared" is the best choice because it demonstrates that this "appearance" happened and stopped in the past, before another thing (realization) from the past.

A, B and C can be eliminated.

I would pick D
_________________

Thanks & Regards,
Anaira Mitch

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

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02 Sep 2017, 08:24
arorag 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

had done is used with did and have done

a big lession is here

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Re: Ozone, a special form of oxygen that screens out harmful ultraviolet r   [#permalink] 02 Sep 2017, 08:24

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