Sixty-five million years ago, according to some scientists

[RonPurewal]

Sure.

[eggpain24]

well, choice e says:
an event that caused the plant and animal extinctions that mark...

the boldface part is an 'essential modifier': a relative clause that MUST modify the immediately preceding noun, in this case 'extinctions'. these sorts of modifiers - 'that' without a comma - follow exactly the same rule that you (hopefully) use for 'which' following a comma: as stated above, they must modify the immediately preceding noun.

since the immediately preceding noun in this case is 'extinctions', you need a plural verb.

incidentally, i find the use of the present tense 'mark' to be a bit bizarre; in my opinion it would make mone sense to say 'marked' instead, as the events we're talking about are clearly in the past.

I think mark（simple present）is used to indicate timeless truth

plant and animal extinctions mark the end of the geologic era known as the Cretaceous Period（it is eternally true because it is like some stuff of indisputable history）

[tim]

That seems like an adequate way to think about this.

[RonPurewal]

I think mark（simple present）is used to indicate timeless truth

plant and animal extinctions mark the end of the geologic era known as the Cretaceous Period（it is eternally true because it is like some stuff of indisputable history）

Yes.

They're not ever going to stop "marking" that point in time. So, exactly correct.

[evelynho]

in general, this seemingly extraneous use of 'the' is indicated if the sentence refers to very specific events, items, etc., particularly if those events/items/etc are assumed to be known to the reader. more so if the events/items/etc form a complete set.
in this problem, these things all make sense. (as for the last point, the form of the correct sentence allows us to infer that the asteroid impact caused all of the plant and animal extinctions that ended the cretaceous period.

if you're worrying about how you'll ever distinguish between sentences that need this 'the' and sentences that don't, then don't worry: you'll never have to make that decision. the gmat won't make you decide between two choices that are both grammatically correct based on such a subtle semantic difference, so there will be some other grammatical error that disqualifies the wrong answers (as in this problem).
so just realize that this form is acceptable, DON'T use it to disqualify an answer choice, and go from there.

Hello Ron,

Thank you for the elabroate explanation.

I do not mean to deepen this minor distinction but I really do not understand the difference you mentioned above.

e.g.
Schistosomiasis, a disease caused by a parasitic worm, is prevalent in hot, humid climates, and it has bcome more widespread as irrigation projects have enlarged the habitat of THE freshwater snails that are the parasite's hosts for part of its life cycle.

Is the definite article here necessary or not before freshwater snails? Can I remove it? Please help to clarify. Thank you.

[RonPurewal]

I do not mean to deepen this minor distinction...

...then don't.
(:

remember, the presence or absence of 'a'/'an'/'the' is not even tested on this exam.
so, in other words, this is a tiny little insignificant nuance of a topic that's entirely out of bounds in the first place.

thus there is no possible benefit in continuing to think about it.

[RonPurewal]

thus there is no possible benefit in continuing to think about it.

^^ in fact, 'no benefit' is the BEST-case scenario here.

heed the warning in red letters here:
https://www.manhattanprep.com/gmat/foru ... ml#p117778

[evelynho]

thus there is no possible benefit in continuing to think about it.

^^ in fact, 'no benefit' is the BEST-case scenario here.

heed the warning in red letters here:
https://www.manhattanprep.com/gmat/foru ... ml#p117778

I can see the no benefit there - get worse at SC, so I will stop to get better.
Thank you and Happy New Year~

[RonPurewal]

you too!

[harika.apu]

Hello Ron ,
I still could not understand why D is incorrect .
Cannot 'it' refer to the event (relative clause ) of first clause ?

Thanks

[RonPurewal]

even if you read the sentence that way, you would still need parallelism:
...that caused plant and animal extinctions and that marks the end of xxxx
in choice D those parts are non-parallel, so, choice D is wrong.

also, it should be plain that this is the wrong interpretation anyway (since, in this interpretation, there is no point in mentioning the plant and animal extinctions -- if you read the sentence that way, the extinctions aren't related to anything else!)

[harika.apu]

even if you read the sentence that way, you would still need parallelism:
...that caused plant and animal extinctions and that marks the end of xxxx
in choice D those parts are non-parallel, so, choice D is wrong.

also, it should be plain that this is the wrong interpretation anyway (since, in this interpretation, there is no point in mentioning the plant and animal extinctions -- if you read the sentence that way, the extinctions aren't related to anything else!)

Yes understood

[RonPurewal]

excellent.

[AmanJ289]

Sixty-five million years ago, according to some scientists, an asteroid bigger than Mount Everest slammed into North America, an event that caused the plant and animal extinctions that mark the end of the geologic era known as the Cretaceous Period.


For, option E, an event that caused the plant and animal extinctions that mark:

Here, we can write it as
an event:
that caused the plant and animal extinctions
that mark
Both that refers back to an event, hence shouldnt we use marks instead of mark (Singular since we are talking about a specific event)

Also,
Sixty-five million years ago, according to some scientists, an asteroid bigger than Mount Everest slammed into North America, causing the plant and animal extinctions and marking the end of the geologic era known as the Cretaceous Period.

be the right answer?

[RonPurewal]

the extinctions "mark the end of the era". (eras in prehistory are defined by the plants, animals, and landforms ON the earth, not by astronomical events.)