Hello Everyone!
This is a great example of a GMAT question that focuses on idiomatic structure and parallelism! Let's take a closer look at the original question and highlight the major differences between options in orange:
Along the major rivers that traverse the deserts of northeast Africa, the Middle East, and northwest India, the combination of a reliable supply of water and good growing conditions both encouraged farming traditions that, in places, endure in at least 6,000 years.
(A) good growing conditions both encouraged farming traditions that, in places, endure in
(B) good growing conditions encouraged farming traditions that have, in places, endured for
(C) of good growing conditions have encouraged farming traditions that, in places, endured for
(D) of good growing conditions both encouraged farming traditions that have, in places, endured
(E) of good growing conditions encouraged farming traditions that have, in places, been enduring for
After a quick glance over the options, there are 3 main things we can focus on:
1. good / of good (parallelism/idioms)
2. both encouraged / encouraged / have encouraged (verb tense/idioms)
3. endure in / endured for / endured / enduring for (idioms)
Since #1 on our list will eliminate 2-3 options right away, let's start there. When we look at the sentence as a whole, we see that we're talking about a combination of 2 items here: a reliable supply of water and good growing conditions. The proper idiomatic structure for this would be the following:
a combination of X and Y
Let's see which options do this correctly, and rule out the ones that don't:
(A) good growing conditions both encouraged farming traditions that, in places, endure in --> a combination of X and Y both = WRONG
(B) good growing conditions encouraged farming traditions that have, in places, endured for --> a combination of X and Y = GOOD
(C) of good growing conditions have encouraged farming traditions that, in places, endured for --> a combination of X and of Y = WRONG
(D) of good growing conditions both encouraged farming traditions that have, in places, endured --> a combination of X and of Y both = WRONG
(E) of good growing conditions encouraged farming traditions that have, in places, been enduring for --> a combination of X and of Y = WRONG
There you go! Option B is the correct choice because it's the only one that uses the proper idiomatic format for "a combination of X and Y!"
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Wonder what would've happened if we focused on another part of the list instead? Let's see what would happen if we focused on #3 on our list: endure in / endured for / endured / enduring for:
(A) good growing conditions both encouraged farming traditions that, in places, endure in
This is INCORRECT. It's not idiomatically correct to say something "endures in" a certain number of years. We say that things "endure for" a certain number of years!
(B) good growing conditions encouraged farming traditions that have, in places, endured for
This is still CORRECT because it's proper to say something "endured for" a number of years. Also, by using past perfect tense (have endured), it's clear that these farming traditions started 6,000 years ago, and they're still being used today.
(C) of good growing conditions have encouraged farming traditions that, in places, endured for
This is INCORRECT because it uses plain past tense, which means the farming traditions started in the past and ended in the past. The intended meaning of the original sentence was to say that these traditions started in the past and are still going on today.
(D) of good growing conditions both encouraged farming traditions that have, in places, endured
This is INCORRECT because it doesn't make sense to say that farming traditions "endured 6,000 years." It's not idiomatically correct - we say that things "endured for" an amount of time.
(E) of good growing conditions encouraged farming traditions that have, in places, been enduring for
While this is OKAY, based on the idiomatic "enduring for" and the use of present perfect continuous tense, we would eventually have to rule it out as INCORRECT because it doesn't use the idiomatic "combination of X and Y" structure correctly.
In the end, option B is still the correct choice!
Don't study for the GMAT. Train for it.