We need a plural verb ‘allow’ for the plural subject of the clause after the semicolon. Drop B, C, and D. There is no need to repeat the infinitive marker’ to’ in as done in E. Therefore A.
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Correct answer must be (A) , for the highlighted errors in other options as excellently explained by daagh ...
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Daagh,

I chose E-Is it not more parallel-to X and to Y?

You are not going into the meaning.

We are given

a narrow waist and a midsection :
1. allow us to swing our arms
2. prevent us from zigzagging on the trail
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Taken from New York Times. [LINK]

Springlike ligaments and tendons in the feet and legs are crucial for running. (Our close relatives the chimpanzee and the ape don’t have them.) A narrow waist and a midsection that can turn allow us to swing our arms and prevent us from zigzagging on the trail. Humans also have a far more developed sense of balance, an advantage that keeps the head stable as we run. And most humans can store about 20 miles’ worth of glycogen in their muscles.
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If NYT reporters or even if their editors were to write GMAT, they may not have got beyond 500. Let me reproduce the relevant part from the horse's' mouth.



1.The highlighted part does not look a sentence at all. It is no more than a bit (fragment) of a sentence, just a noun phrase enveloped between two periods. It is not also a modifier and since there seems to be no attached noun.

Keeping it aside these for a while, probably we can make some sense out of the phrase if we can parse it as follows.

1. The narrow waist and midsection(the doers of the three actions) can 1. Turn, 2. Allow us to swing our arms, and 3. prevent us from zigzagging.

If the above were a plausible interpretation, then the text has missed a comma after 'turn' and a comma before 'and'

There is no way we can take 'turn allow' us as a single verb.
It is also not tenable that 'prevent us' can be a full -fledged function.
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The construction is "X and Y are" or "X and Y have"

X and Y =compound subject + plural verb

A

Can u tell me why to prevent not required . in solution everyone said not required but didnt provide reason to support it

Hi...




Let’s break the sentence (after fitting choice E) and understand the intended meaning:

Humans are better adapted for running than are other primates;
a narrow waist and a midsection that can turn allow us
to swing our arms
and to prevent us from zigzagging on the trail.

• So, “and” is supposed to join two clauses and the subject of both the clauses is same:
• Subject(plural) : a narrow waist and a midsection that can turn (“that can turn” is a modifier for “midsection”). Now let's remove the modifier and see what happens to the sentence.
• Clause 1: a narrow waist and a midsection…… allow us to swing our arms
• and
• Clause 2: a narrow waist and a midsection……. to prevent us from zigzagging….

• Clearly , the “to prevent” is not a verb. So the part before “and” is a clause and the part after “and” is not a clause (since it has no verb). Thus, a parallelism error arises here.
• Without the “to”, the part after “and” becomes a clause and makes sense:
• “…a narrow waist and a midsection …..prevent us from zigzagging


Hope this helps
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Hi Aman

Let us plug in option (E) into the sentence and read the whole thing.

Humans are better adapted for running than are other primates; a narrow waist and a midsection that can turn allow us to swing our arms and to prevent us from zigzagging on the trail.

If we structure the sentence this way, the "narrow waist" and "midsection that can turn" work such that they "allow us" to (what they "allow" must apply to both the below if we begin both with "to"):

a) to swing our arms
b) to prevent us from zigzagging

However, (b) does not make sense - the narrow waist and midsection that can turn do not "allow us to prevent us from zigzagging". They:

a) allow us to swing our arms
b) prevent us from zigzagging

Therefore, the "to" must appear only before "swing" and not before "prevent".

Hope this helps.
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