Ozone reaches high concentrations twelve miles

[RAHULS852]

Applying these thoughts to those problems, note that the ozone problem doesn't give you a choice between 'had appeared' and simply 'appeared'. Here, the 'had' emphasizes that the appearing took place before the realization, but I think 'appeared' would be fine also. It's not that common to use past perfect for an event before present perfect. The more common pairing is past perfect and past simple.

Ok. Since Ist problem did not have option of simple past, use of "had appeared" is fine.

So below mentioned sentence would be fine:

Ozone reaches high concentrations twelve miles above Earth, where it appeared immune to human influence; we have now realized, though, that emissions of industrial chlorofluorocarbons deplete the ozone layer.

Not sure exactly what you mean by 'point event', but if you mean 'action that took place in the past and is now finished' then we'd need to use the past simple. If we wanted to state that the suggesting took place in the past and is finished now, we'd need to say 'Some art historians once suggested that Impressionism..

I did not get your point about above highlighted portion.
"Have + ed" means that

(a) action that took place in the past and is now finished
Tarun has completed his graduation from Harvard Business School.

Here we don't know that when has tarun completed his graduation. May be 10 years ago or recently but effect of completion is relevant to present.

Russia and the U.S. have sent expeditions to the moon. ( This event happened over forty years ago but it's relevant to the current topic of discussion)

(b) action took place till recent past but definitely not going on in present

I have lived in NYC for 2 years ( means I lived in NYC till now but now I am not living anymore)

Simple past is a past event that completed in the past and it's not relevant to present.

Tarun completed his graduation in 2008.

Kindly review my understanding.

Regards,
Rahul Singh

[Sage Pearce-Higgins]

So below mentioned sentence would be fine:

Ozone reaches high concentrations twelve miles above Earth, where it appeared immune to human influence; we have now realized, though, that emissions of industrial chlorofluorocarbons deplete the ozone layer.

Yes, I think that sentence is okay, although not as clear as the correct answer choice. Just remember that we're dealing with meaning and emphasis. Both these concepts are not mathematically precise.

(b) action took place till recent past but definitely not going on in present

I have lived in NYC for 2 years ( means I lived in NYC till now but now I am not living anymore)

This isn't true. Present perfect is often used for events that started in the past but are still going on now. Please reread my description of present perfect in my last post and check out the relevant chapter in the SC strategy guide. The sentence 'I have lived in NYC for 2 years' means that I still live in NYC. I think this is the gap in your understanding.

[RAHULS852]

This isn't true. Present perfect is often used for events that started in the past but are still going on now. Please reread my description of present perfect in my last post and check out the relevant chapter in the SC strategy guide. The sentence 'I have lived in NYC for 2 years' means that I still live in NYC. I think this is the gap in your understanding.

But Ron's post on 1st page said a different thing.

https://www.manhattanprep.com/gmat/foru ... t3584.html

In fact Ron mentioned the same statement in few other posts about present perfect

"present perfect = still going" is generally restricted to sentences in which the actual timeframe is given.
https://www.manhattanprep.com/gmat/foru ... t9670.html

A) I have lived in Florida. ( here it means that I no longer live in Florida. If i still live then I will write "I live in Florida")
B) I have lived in Florida for 2 years ( Here it can represent a ongoing state that I might live in Florida)

Then 3 types of usage for present perfect:
1) It happened & is relevant to present.

2) If "has +ed" used with time duration then that thing happened for that duration upto now.

he sentence 'I have lived in NYC for 2 years' means that I still live in NYC

3) If it's an ongoing state verb, then "has/have VERBed" without an explicit time period means ...
... it's happened before,
... it's not happening now
example (A) above
These all things I learned from Ron's post.
Kindly correct me If I misinterpreted anything.

Regards,
Rahul Singh

[Sage Pearce-Higgins]

But Ron's post on 1st page said a different thing.

https://www.manhattanprep.com/gmat/foru ... t3584.html

You're going to need to be more specific when you quote; I can't find the reference here.

In fact Ron mentioned the same statement in few other posts about present perfect

"present perfect = still going" is generally restricted to sentences in which the actual timeframe is given.
https://www.manhattanprep.com/gmat/foru ... t9670.html

Sure, I agree. However, note the phrase 'generally restricted' - it's not a solid rule.

A) I have lived in Florida. ( here it means that I no longer live in Florida. If i still live then I will write "I live in Florida")
B) I have lived in Florida for 2 years ( Here it can represent a ongoing state that I might live in Florida)

Agreed about (A); however, (B) means that you definitely live in Florida now (or at least 99% certain).

Concerning 'point events', I can see where you're getting at now that I've read Ron's posts. I think that may be complicating the issue, as we then have to decide whether something is a 'point event'. It seems that the main issue going on here is the nature of the use of present perfect in the phrase 'Art historians have suggested that Impressionism...'. I guess that you want to say that this is a 'point event' and so justifies the use of past perfect later on in the sentence, in the same way that the 'we have now realized...' does. This is a tough one. We could argue about whether 'suggested' is a 'point event'. I might argue that it isn't, as it's more similar to an action like saying or thinking. To be honest, the likelihood of you getting something out of this debate that will help your future test performance is quite slim.

I encourage you to think more simply: past perfect is for showing the 'past before the past'. So we need it when the order of events is in doubt, or to emphasize the order of events. If you don't need it, then just use past simple as a default option.

[RAHULS852]

I encourage you to think more simply: past perfect is for showing the 'past before the past'. So we need it when the order of events is in doubt, or to emphasize the order of events. If you don't need it, then just use past simple as a default option.

I should not complicate this issue further. I got your point about highlighted portion.
Thanks Sage.

Regards,
Rahul Singh

[Sage Pearce-Higgins]

No problem.