Manipulating ecosystems to wipe out disease-carrying mosquitoes seems

OFFICIAL EXPLANATION



THE PROMPT


• Meaning?
Manipulating ecosystems to wipe out disease-carrying mosquitoes
(1) seems to be a good way to eradicate malaria quickly, and
(2) [is] an idea whose benefits outweigh its environmental costs

• Structure of this sentence?
Let's look at the part at the end and correct a pronoun error: "an idea whose benefits outweigh its environmental costs."

→ That whole thing is called a summative modifier.
The writer makes up a word (usually a noun phrase) that "summarizes" or encapsulates the idea expressed in the previous clause (hence "summative").
This noun phrase describes the noun-thing that happened in the previous clause and gives more detail about that clause.
A summative modifier is a special kind of appositive.

→ Why am I talking about this issue even though it is not a decision point?
GMAC likes to test these summative modifiers.
They are integral to sophisticated prose.
If you see a strange-looking modifier (or bunch of words that appear to be "tacked on" to the sentence), check to see whether that modifier or that bunch of words uses a noun phrase to capture the idea expressed in the previous clause.
→ in this case, "an idea" refers to the fact that manipulating ecosystems to wipe out disease-carrying mosquitoes seems to be a good way to eliminate malaria quickly.

THE OPTIONS


• noun/pronoun disagreement
→ what thing has benefits and costs? An idea.
→ an idea is singular. Its benefits outweigh ITS costs. (Not their.)
That is, the plural their cannot refer back to the singular idea
ELIMINATE A


• subject-verb agreement
→ The singular subject manipulating ecosystems requires the singular verb seems (not seem).
ELIMINATE B


• that creates a nonsensical sentence
→ With the full sentence, we have
Manipulating ecosystems that wipe out disease-carrying mosquitoes

→ The ecosystems themselves do not wipe out the mosquitoes.

• what does whose refer to?
I suppose we could argue that the only logical candidate is manipulating ecosystems.
That whose is a long way from the noun it allegedly describes; noun modifiers should be as close as possible to their nouns.
The meaning problem, above, is fatal. This one is harder to analyze. Pick one error and move on.
ELIMINATE C


• subject-verb agreement
→ The singular subject manipulating ecosystems requires the singular verb seems (not seem).

• noun/pronoun disagreement
The benefits of the idea outweigh the costs of the idea, requiring the singular its to refer to the singular idea.
ELIMINATE D


• I do not see any errors
• the singular verb seems is correctly paired with its singular subject, "manipulating ecosystems to wipe out disease-carrying mosquitoes."
(Gerund clauses -- verbING clauses in which the verbING acts as a noun -- are always singular.)
• the pronoun usage is correct.
→ the idea's benefits (its benefits) outweigh the idea's (its ideas) environmental costs.

The answer is E.

COMMENTS

We have a nice collection of veterans and newcomers, all of whom wrote answers with good analysis.

Keep up the good work.
Kudos to all.