Hi @abhasjha,
Thanks for the message - I'm happy to respond to this one.
Let's solve this question using the e-GMAT three-step process.
Meaning Analysis
"¢ Providing initial evidence that airports are a larger source of pollution than they were once believed to be,
Okay, so this sentence starts by telling us that someone has provided initial evidence that airports cause more pollution that it was once believed they did. Who has provided this proof? Let's read on to find out.
"¢ environmentalists in Chicago report
As anticipated, the next part of the sentence tells us who has provided this proof: environmentalists in Chicago. Let's read on to find out what these environmentalists report.
"¢ that the total amount of pollutant emitted annually by vehicles at O'Hare International Airport is twice as much as that which is being emitted annually by all motor vehicles in the Chicago metropolitan area.
So this is the evidence that the environmentalists have given: vehicles at a particular airport give out a total amount of pollution every year that is double the amount of the pollution given out every year by all the automobiles in the Chicago city area.
The meaning here is absolutely clear:
1. Environmentalists in Chicago have provided some initial evidence that shows that airports cause more pollution than they were believed to.
2. These environmentalists report that the amount of pollution caused by the traffic at O'Hare Airport is double the amount of pollution caused by vehicles in the city.
Having established the meaning, let's analyze this sentence for errors.
Error Analysis
"¢ Providing initial evidence
o that airports are a larger source of pollution
 than they were once believed to be,
"¢ environmentalists in Chicago report
o that the total amount of pollutant emitted annually by vehicles at O'Hare International Airport is twice as much as
 that which is being emitted annually by all motor vehicles in the Chicago metropolitan area.
This sentence has five clauses (i.e., subject-verb pairs). All the pairs make meaningful sense, and there are no verb tense issues.
However, there is a comparison issue in this sentence. Always remember that comparisons have to be both logically and grammatically parallel. This sentence presents a comparison using the comparison marker "as much as". So, the two elements connected by this marker must be both logically and grammatically parallel. These two elements are:
1. the total amount of pollutant emitted annually by vehicles at O'Hare International Airport
2. that which is being emitted annually by all motor vehicles in the Chicago metropolitan area.
Let's first look at the structure of the first element. It starts with a noun phrase, "the total amount of pollutant". This phrase is followed by a verb-ed modifier, "emitted". A noun and its modifier together form a phrase. So, this part of the comparison is a PHRASE. Grammatically, it can only be parallel to another phrase.
When we compare this structure to that of the second element, we find that they do not match. The second element starts with "that". In this context, "that" correctly stands for "the total amount of pollutant". However, "that" is followed by "which". "Which" is a relative pronoun modifier that starts a clause. In this case, it is the subject of the verb "is". So, this part of the sentence is a CLAUSE. A clause cannot be parallel to a phrase. So, there's a parallelism issue here. While the two entities are logically parallel, they don't match in terms of grammar.
Having done the error analysis, let's proceed to the options.
Process of Elimination
Option A: INCORRECT as discussed in the error analysis.
Option B: INCORRECT.
1.
Adverb Error: 'Annually' is placed next to 'as much'. According to the intended meaning of the sentence, 'annually' should refer to 'emitted'.
2.
Comparison Error: 'The total amount of pollutant emitted annually by vehicles at the O'Hare International Airport' should be compared with 'the total amount of pollutant emitted annually by all motor vehicles in the Chicago metropolitan area'. In the absence of 'that', there is no noun entity that is parallel to 'the total amount of pollutant'. Also, the verb 'is' has no counterpart in the first element of comparison.
Option C: INCORRECT
1.
Idiom Error: 'As much' is not the correct idiom for comparison. It should be 'as much as'.
2.
Redundancy error: 'As much' and 'compared to' are both terms that are used to compare items. It is incorrect to use two terms that indicate the same meaning.
3.
Parallelism Error: 'What is' is a CLAUSE and cannot be parallel to a PHRASE.
Option D: CORRECT
Note how this choice resolves the parallelism error in the original. 'That emitted annually' is perfectly parallel to 'the total amount of pollutant emitted annually'. Also, this choice is more concise than the original sentence. Since 'twice' already indicates that the first amount is double the other, there is no need to use the phrase 'as much as'.
Option E: INCORRECT
1.
Comparison Error: This is a pretty interesting choice! It perfectly resolves the grammatical parallelism issue from the original sentence. However, it introduces an ILLOGICAL comparison. Now, the total amount of pollution caused by vehicles at the airport is illogically being compared to motor vehicles in Chicago. This comparison makes no meaningful sense.
I hope this analysis helps! Next time you're stuck with a challenging question, try the e-GMAT three-step process to solve the question. I guarantee that it'll help. To start learning right away, you can register at
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Regards,
Meghna
