Pack 9 Q3: The use of Bt corn, which is corn that has been modified...

The original sentence has Subject-verb error.
The use of BT corn, ......, has reduced.., and have decreased.... So A is out
A. have decreased the occurrence of pests in entire regions where it is planted

We will also eliminate the other choices with the same error
D. have decreased the occurrence of pests in entire regions where planted

Remaining choices B, C, E

B. has decreased the occurrence of pests in entire regions where they are planted
Now this has sorted out the original problem of SV agreement, but 'they' refers to pests (does not make sense) or bt corn (makes sense but is singular). Either way this is gone.

C. has decreased the occurrence of pests in entire regions where the corn is planted
This looks good. SV agreement is good, the pronoun reference problem is also sorted. Lets keep this.


E. Bt corn plants have decreased the occurrence of pests in entire regions where it is planted
Here there is an obvious error that singular pronoun "it" refers to plants. E is out. There are other errors too, but no point wasting time after we have got an obvious error.

My choice is C option
Area tested- Subject- Verb
BT Corn is a singular noun, therefore it requires HAS rather than HAVE.
Eliminate A and C
A. have decreased the occurrence of pests in entire regions where it is planted- incorrect

B. has decreased the occurrence of pests in entire regions where they are planted- incorrect
They are- Plural and BT corn is a singular noun.

C. has decreased the occurrence of pests in entire regions where the corn is planted- correct- Correct

D. have decreased the occurrence of pests in entire regions where planted- incorrect

E. Bt corn plants have decreased the occurrence of pests in entire regions where it is planted- incorrect

Subject -- "use"
Verb 1 -- has reduced
Verb 2 -- should be parallel with verb 1 and also follow the subject verb agreement rule i.e. we would need a singular verb.

A. have decreased the occurrence of pests in entire regions where it is planted -- Eliminated. SV error.
B. has decreased the occurrence of pests in entire regions where they are planted -- Pronoun ambiguity. "They" may incorrectly refer back to pesticide or pests. Although it isn't a hard and fast rule but in this case, we need the "they" to refer to "BT Corn Plants". This is eliminated in light of C.
C. has decreased the occurrence of pests in entire regions where the corn is planted -- Fixes the issue in B. Correct choice.
D. have decreased the occurrence of pests in entire regions where planted -- Eliminated. SV error.
E. Bt corn plants have decreased the occurrence of pests in entire regions where it is planted -- Eliminated. Meaning error. Bt corn plants have not decreased anything. The "use" of BT corn plants has decreased the occurrence.

Official Explanation

The use of Bt corn, which is corn that has been modified to produce insecticidal proteins that occur naturally in the bacterium Bacillus thuringiensis, has reduced the producers’ use of pesticides by more than 36 percent and have decreased the occurrence of pests in entire regions where it is planted.

A. have decreased the occurrence of pests in entire regions where it is planted
B. has decreased the occurrence of pests in entire regions where they are planted
C. has decreased the occurrence of pests in entire regions where the corn is planted
D. have decreased the occurrence of pests in entire regions where planted
E. Bt corn plants have decreased the occurrence of pests in entire regions where it is planted

After a quick glance over the options, there are 2 main areas we can focus on:
1. have decreased / has decreased (Subject-Verb Agreement)
2. it is planted / they are planted / the corn is planted / planted (Pronouns & Clarity)

Since #1 on our list is a clear “either/or” split, let’s start there. We need to make sure the verb (have/has decreased) matches up with the subject (use). Since “use” is singular, let’s eliminate any options that use a plural verb:

A. have decreased the occurrence of pests in entire regions where it is planted
B. has decreased the occurrence of pests in entire regions where they are planted
C. has decreased the occurrence of pests in entire regions where the corn is planted
D. have decreased the occurrence of pests in entire regions where planted
E. Bt corn plants have decreased the occurrence of pests in entire regions where it is planted

We can eliminate options A & D because they use a plural verb with a singular subject.

Option E uses the wrong verb tense, but there is something else wrong with it: the structure. If we cross out the modifier phrase, you’ll see that what’s left over doesn’t work as a complete sentence:

The use of Bt corn, which is corn that has been modified to produce insecticidal proteins that occur naturally in the bacterium Bacillus thuringiensis, has reduced the producers’ use of pesticides by more than 36 percent and Bt corn plants have decreased the occurrence of pests in entire regions where it is planted.

By changing the wording, this has now become 2 independent clauses that need to be separated by a comma and conjunction - but there is no comma. It also changes the meaning of the second clause to be about “Bt corn” instead of “the use of Bt corn.” So we also need to eliminate this one.

Now that we have it narrowed down to only 2 options, let’s tackle #2 on our list: clarity & pronouns. We need to make sure that any pronouns have 100% clear antecedents, and we also need to check that the meaning doesn’t get distorted:

B. has decreased the occurrence of pests in entire regions where they are planted
This is INCORRECT because the pronoun “they” doesn’t have a clear antecedent. Is it referring back to pests, corn, pesticides, etc.? If it’s not 100% clear, it’s a vague pronoun - and the GMAT does not like vague pronouns.

C. has decreased the occurrence of pests in entire regions where the corn is planted
This is CORRECT! The subject-verb agreement with “use” and “has decreased” works, and it does away with pronouns entirely and simply repeats the noun that the verb “is planted” applies to. The meaning is 100% clear, so this is our answer.

There you have it - option C is the correct choice! By focusing on key differences and starting with an “either/or” split, we can narrow down our choices quickly.


Don’t study for the GMAT. Train for it.

Well done, XyLan! You cracked the code! Kudos to you!

Well done, sauravleo123! You cracked the code on both the subject-verb agreement and vague pronouns! Kudos to you!

Well done, AnirudhaS! You cracked the code on this one! Kudos to you!

Well done, thenikhilseth! You cracked the code on this one! I can't wait to see more explanations from you on future questions!

Well done, ravigupta2912! You cracked the code! I look forward to more great explanations in future questions!