GMAT Question of the Day - Daily to your Mailbox; hard ones only

 It is currently 18 Jul 2018, 13:32

### GMAT Club Daily Prep

#### Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

# QOTD: Leaf beetles damage willow trees by

Author Message
TAGS:

### Hide Tags

MBA Section Director
Joined: 19 Mar 2012
Posts: 5128
Location: India
GMAT 1: 760 Q50 V42
GPA: 3.8
WE: Marketing (Non-Profit and Government)
QOTD: Leaf beetles damage willow trees by [#permalink]

### Show Tags

02 Aug 2017, 12:11
5
11
00:00

Difficulty:

55% (hard)

Question Stats:

64% (01:39) correct 36% (02:23) wrong based on 755 sessions

### HideShow timer Statistics

Verbal Question of The Day: Day 73: Critical Reasoning

Subscribe to GMAT Question of the Day: E-mail | RSS

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

Every question of the day will be followed by an expert reply by GMATNinja in 12-15 hours. Stay tuned! Post your answers and explanations to earn kudos.

_________________
GMAT Club Verbal Expert
Status: GMAT and GRE tutor
Joined: 13 Aug 2009
Posts: 1825
Location: United States
GMAT 1: 780 Q51 V46
GMAT 2: 800 Q51 V51
GRE 1: Q170 V170
Re: QOTD: Leaf beetles damage willow trees by [#permalink]

### Show Tags

02 Aug 2017, 12:13
4
The conclusion is that "the researchers’ discovery probably does explain why leaf beetles cause particularly severe damage to willows in areas with severe air pollution." How do we arrive at that conclusion?

• "Leaf beetles damage willow trees by stripping away their leaves."
• "A combination of parasites and predators generally keeps populations of these beetles in check." Thus, the parasites and predators help limit the amount of beetles and, presumably, the damage done to the willows.
• "Researchers have found that severe air pollution results in reduced predator populations." A reduction in predator populations would be good for the leaf beetles. But with fewer predators to keep the beetles in check, the willow trees might suffer. So, air pollution sounds bad for the willow trees and good for the leaf beetles, but we do not know the extent of this effect.
• "The parasites, by contrast, are not adversely affected by pollution." Thus, air pollution would have no effect on the parasites and thus no effect on the leaf beetles. So, according to the information in the passage, air pollution would not affect the willow trees or the leaf beetles.

Okay, so if air pollution only affects one of the two factors that keep the beetle populations in check, why are the beetles still able to cause particularly severe damage to willows in areas with severe air pollution? Shouldn't the parasites keep the beetle populations in check and thus prevent the beetles from causing particularly severe damage to the trees? We need something else to explain this phenomenon:

Quote:
(A) neither the predators nor the parasites of leaf beetles themselves attack willow trees

We need to explain why the beetles are still able to cause significant damage despite the presence of parasites that keep the beetle populations in check. We don't care whether the predators or parasites damage the willow trees directly. Choice (A) is irrelevant and can be eliminated.

Quote:
(B) the parasites that attack leaf beetles actually tend to be more prevalent in areas with severe air pollution than they are elsewhere

If there are more parasites in areas with severe air pollution, then those parasites would further help to LIMIT the beetle populations. This effect should REDUCE the amount of damage done by the beetles to the willows. Thus, statement (B) does not explain why the beetles can cause particularly severe damage in areas with severe air pollution. Eliminate (B).

Quote:
(C) the damage caused by leaf beetles is usually not enough to kill a willow tree outright

We don't care whether the beetles can KILL a willow tree. We are simply trying to explain why the beetles are able to cause particularly severe DAMAGE to the willow trees. Thus, choice (C) does not help explain the observed phenomenon and can be eliminated.

Quote:
(D) where air pollution is not especially severe, predators have much more impact on leaf-beetle populations than parasites do

We are told that the predator populations are reduced in areas with severe air pollution. If predators affect the leaf-beetle populations MORE than the parasites, it makes sense that the parasites themselves might not have a huge impact on the beetle populations. That would explain why the beetles are still able to cause such damage even though the parasites are still there. Choice (D) looks good.

Quote:
(E) willows often grow in areas where air pollution is especially severe

We don't care about where willows grow and where they do not. All we know is that the beetles cause severe damage to willows in areas with severe air pollution, and choice (E) does not help explain this phenomenon. Eliminate (E).

Choice (D) is our winner.
_________________

GMAT Club Verbal Expert | GMAT/GRE tutor @ www.gmatninja.com (Now hiring!) | GMAT blog | Food blog | Notoriously bad at PMs

Beginners' guides to GMAT verbal
Reading Comprehension | Critical Reasoning | Sentence Correction

Series 1: Fundamentals of SC & CR | Series 2: Developing a Winning GMAT Mindset

SC & CR Questions of the Day (QOTDs), featuring expert explanations
All QOTDs | Subscribe via email | RSS

Hit the request verbal experts' reply button -- and please be specific about your question. Feel free to tag @GMATNinja and @GMATNinjaTwo in your post. Priority is always given to official GMAT questions.

Sentence Correction articles & resources
How to go from great (760) to incredible (780) on GMAT SC | That "-ing" Word Probably Isn't a Verb | That "-ed" Word Might Not Be a Verb, Either | No-BS Guide to GMAT Idioms | "Being" is not the enemy | WTF is "that" doing in my sentence?

Reading Comprehension, Critical Reasoning, and other articles & resources
All GMAT Ninja articles on GMAT Club | Using LSAT for GMAT CR & RC |7 reasons why your actual GMAT scores don't match your practice test scores | How to get 4 additional "fake" GMAT Prep tests for \$29.99 | Time management on verbal

Senior Manager
Joined: 06 Jul 2016
Posts: 417
Location: Singapore
Concentration: Strategy, Finance
Re: QOTD: Leaf beetles damage willow trees by [#permalink]

### Show Tags

02 Aug 2017, 12:45
1
souvik101990 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 ________.

Leaf beetles damage willow trees, but parasites + predators keep the population of these beetles in check.
Severe air pollution => reduced predator population. Parasites not adversely affected.
Researchers find that leaf beetles cause severe damage to willows in areas with severe air pollution.
Why?

Quote:
(A) neither the predators nor the parasites of leaf beetles themselves attack willow trees

This does not explain why the damage is high in areas with severe air pollution. OUT!

Quote:
(B) the parasites that attack leaf beetles actually tend to be more prevalent in areas with severe air pollution than they are elsewhere

And these parasites attack leaf beetles => the damage should be less in areas with severe pollution if the parasites are more prevalent here. OUT!

Quote:
(C) the damage caused by leaf beetles is usually not enough to kill a willow tree outright

This would be same in areas with pollution, or without pollution and again, this doesn't explain the researcher's findings. OUT!

Quote:
(D) where air pollution is not especially severe, predators have much more impact on leaf-beetle populations than parasites do

Predators have much more impact on leaf-beetle population, but in areas with severe pollution, predators numbers decrease. This would explain why the beetles are able to cause more damage to the willow tree leaves.
KEEP!

Quote:
(E) willows often grow in areas where air pollution is especially severe

This doesn't help why the damage would be more in areas where pollution is severe. OUT!

D is the answer for me!
_________________

Put in the work, and that dream score is yours!

VP
Status: Learning
Joined: 20 Dec 2015
Posts: 1206
Location: India
Concentration: Operations, Marketing
GMAT 1: 670 Q48 V36
GRE 1: Q157 V157
GPA: 3.4
WE: Manufacturing and Production (Manufacturing)
Re: QOTD: Leaf beetles damage willow trees by [#permalink]

### Show Tags

03 Aug 2017, 08:07
souvik101990 wrote:

Verbal Question of The Day: Day 73: Critical Reasoning

Subscribe to GMAT Question of the Day: E-mail | RSS

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

Every question of the day will be followed by an expert reply by GMATNinja in 12-15 hours. Stay tuned! Post your answers and explanations to earn kudos.

The argument lists beetles as the cause of the damage of the willows.
Severe pollution can reduce the damage to willow trees by beetles because predator and parasite have detrimental effects on the beetles.

[b]Conclusion : 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

Only D gives us the reasoning why conclusion is correct .

[/b]
_________________

Senior Manager
Joined: 12 Feb 2015
Posts: 327
QOTD: Leaf beetles damage willow trees by [#permalink]

### Show Tags

02 Jun 2018, 17:30
Question Stem:-

1) Leaf beetles:-
1.1) damage willow trees by stripping away their leaves, but -----------> Leaf beetles are BAD for Trees
1.2) a combination of parasites and predators generally keeps populations of these beetles in check--------------> a combination of parasites and predators
does not allow the population of Leaf beetles to explode. -------------->which HELPS trees as lesser no. of Leaf beetles will cause Less damage to trees.

2) Researchers have found that severe air pollution results in reduced predator populations. --------------------> Severe air pollution is reduces predator populations.-----------> Reduced predator population means GOOD for Leaf beetles.

3) The parasites, by contrast, are not adversely affected by pollution; --------------------> Severe air pollution does not affect parasites----------> Does not do any good to Leaf beetles.

nevertheless, the researchers’ discovery probably does explain why leaf beetles cause particularly severe damage to willows in areas with severe air pollution, since ________.

Analysis, "a combination of parasites and predators generally keeps populations of these beetles in check". If say, a combination of, 10 parasites and 10 predators, is required but due to severe air pollution (which affects predator population but does not affect parasite population) the predator population reduces to 5, leading to unavailability of the right combination. This is good for Leaf Beetles as the right combination is not available then Leaf Beetle population will not be kept in check.

Elimination and Selection of right answer choice:-
Option D says--------->where air pollution is NOT especially severe, predators have much more impact on leaf-beetle populations than parasites do----------->Air polution not severe then no impact on predator population----------->which means, as per our hypothetical case above, the required combination, of 10 predators & 10 parasites, is available then these 10 predators have much more impact on leaf-beetle populations than these 10 parasites do which keeps the Leaf Beetle population in check. Hence the right combination is reached and the objective is reached.

Option (D) comes very close to the analysis. No other options speak of the right number required to keep the population of leaf beetles in check.
_________________

"Please hit +1 Kudos if you like this post"

_________________
Manish

"Only I can change my life. No one can do it for me"

Director
Joined: 23 Sep 2015
Posts: 588
Re: QOTD: Leaf beetles damage willow trees by [#permalink]

### Show Tags

19 Jun 2018, 22:27
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.

Pre-thinking :
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. Few speculations:
- May be less parasites found in this area.
- Something else found in area that live on these parasite.
- parasites don't go near willow trees.

(A) neither the predators nor the parasites of leaf beetles themselves attack willow trees --- the duos attack on willow tree is not a matter to talk about. either way it is not affecting.

(B) the parasites that attack leaf beetles actually tend to be more prevalent in areas with severe air pollution than they are elsewhere --- well yes it should be but it is not. actually a contrast to a fact mentioned above, wrong.

(C) the damage caused by leaf beetles is usually not enough to kill a willow tree outright --- irrelevant.

(D) where air pollution is not especially severe, predators have much more impact on leaf-beetle populations than parasites do --- This choice want to say that when no air pollution, predators have much more impact on leaf-beetle populations than parasites do, which means if we remove predators from the picture, parasite will make less impact on beetles' population. this is why beetles are impacting willow trees.

(E) willows often grow in areas where air pollution is especially severe --- this on is not pointing any light on the situation.
_________________

Thanks!
Do give some kudos.

Simple strategy:
“Once you’ve eliminated the impossible, whatever remains, however improbable, must be the truth.”

Best Gmat Resource:
GmatPrep CR|GmatPrep SC|GmatPrep RC

Re: QOTD: Leaf beetles damage willow trees by   [#permalink] 19 Jun 2018, 22:27
Display posts from previous: Sort by

# Events & Promotions

 Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.