AbdurRakib wrote:Which of the following most logically completes the passage?

Leaf beetles damage willow trees by stripping away their leaves, but a combination of parasites and predators generally keeps populations of these beetles in check. Researchers have found that severe air pollution results in reduced predator populations. The parasites, by contrast, are not adversely affected by pollution; nevertheless, the researchers' discovery probably does explain why leaf beetles cause particularly severe damage to willows in areas with severe air pollution, since __________.


A. neither the predators nor the parasites of leaf beetles themselves attack willow trees
B. the parasites that attack leaf beetles actually tend to be more prevalent in areas with severe air pollution than they are elsewhere
C. the damage caused by leaf beetles is usually not enough to kill a willow tree outright
D. where air pollution is not especially severe, predators have much more impact on leaf-beetle populations than parasites do
E. willows often grow in areas where air pollution is especially severe

Please explain

OG Verbal 2017 New Question(Book Question: 146)

AbdurRakib wrote:Which of the following most logically completes the passage?

Leaf beetles damage willow trees by stripping away their leaves, but a combination of parasites and predators generally keeps populations of these beetles in check. Researchers have found that severe air pollution results in reduced predator populations. The parasites, by contrast, are not adversely affected by pollution; nevertheless, the researchers' discovery probably does explain why leaf beetles cause particularly severe damage to willows in areas with severe air pollution, since __________.


A. neither the predators nor the parasites of leaf beetles themselves attack willow trees
B. the parasites that attack leaf beetles actually tend to be more prevalent in areas with severe air pollution than they are elsewhere
C. the damage caused by leaf beetles is usually not enough to kill a willow tree outright
D. where air pollution is not especially severe, predators have much more impact on leaf-beetle populations than parasites do
E. willows often grow in areas where air pollution is especially severe

GMATGuruNY wrote:

AbdurRakib wrote:Which of the following most logically completes the passage?

Leaf beetles damage willow trees by stripping away their leaves, but a combination of parasites and predators generally keeps populations of these beetles in check. Researchers have found that severe air pollution results in reduced predator populations. The parasites, by contrast, are not adversely affected by pollution; nevertheless, the researchers' discovery probably does explain why leaf beetles cause particularly severe damage to willows in areas with severe air pollution, since __________.


A. neither the predators nor the parasites of leaf beetles themselves attack willow trees
B. the parasites that attack leaf beetles actually tend to be more prevalent in areas with severe air pollution than they are elsewhere
C. the damage caused by leaf beetles is usually not enough to kill a willow tree outright
D. where air pollution is not especially severe, predators have much more impact on leaf-beetle populations than parasites do
E. willows often grow in areas where air pollution is especially severe

Fact 1: Of the two elements that keep leaf beetle populations in check -- predators and parasites -- only predators are adversely affected by severe air pollution.
Fact 2: In areas with severe air pollution, leaf beetles cause particularly severe damage to willows.

The correct answer choice must explain why leaf beetles cause particularly severe damage to willows in areas with severe air pollution, even though air pollution does not adversely affect parasites.

D: Predators have much more impact on leaf-beetle populations than parasites do.
Here, predators are MORE IMPORTANT than parasites, explaining why parasites alone are not able to prevent leaf beetles from damaging willows in areas with severe air pollution.

The correct answer is D.

B: The parasites that attack leaf beetles actually tend to be more prevalent in areas with severe air pollution than they are elsewhere.
Implication:
In areas with severe air pollution, the prevalence of parasites should be sufficient to prevent leaf beetles from damaging willows -- CONTRADICTING FACT 2, which indicates particularly severe damage in these areas.
A fact is a statement not in dispute; it cannot be contradicted.
Eliminate B.

Mo2men wrote:Dear Mitch,

How can I negate the OA to check if it is correct answer? Should l I negate also 'where air pollution is not especially severe'??
Thanks

RBBmba@2014 wrote:Hi Experts,
Got a quick question on the OA:

Here, the Option D states that "where air pollution is NOT especially severe predators have much more impact than parasites ", but per the passage, I guess, we're concerned with the areas where air pollution is severe. Isn't it ?

So, how the Option D is correct ?