GMAT Critical Reasoning weaken questions are one of the most popular question type that is tested in GMAT CAT.

Weaken

"Beverage company representative: The plastic rings that hold six-packs of beverage cans together pose a threat to wild animals, which often become entangled in the discarded rings and suffocate as a result. Following our lead, all beverage companies will soon use only those rings consisting of a new plastic that disintegrates after only three days’ exposure to sunlight. Once we all complete the switchover from the old to the new plastic rings, therefore, the threat of suffocation that plastic rings pose to wild animals will be eliminated."

Which one of the following, if true, most seriously weakens the representative’s argument - Question

(A) The switchover to the new plastic rings will take at least two more years to complete.
(B) After the beverage companies have switched over to the new plastic rings, a substantial number of the old plastic rings will persist in most aquatic and woodland environments.
(C) The new plastic rings are slightly less expensive than the old rings.
(D) The new plastic rings rarely disintegrate during shipping of beverage six-packs because most trucks that transport canned beverages protect their cargo from sunlight.
(E) The new plastic rings disintegrate into substances that are harmful to aquatic animals when ingested in substantial quantities by them.

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Step 1 : Read the question before reading the stimulus

Note: 
This will save at least 30 seconds of your time in each gmat critical
reasoning question. Multiply 30 by 15 and you can save at least 7.5
minutes.

Step 2:  Identify the type of critical reasoning question being tested

Step 3:  Here the question type being tested is Weaken question.

Note : Other Weaken question formats

1. Which of the following, if true, most weakens  the argument?
2. Which of the following, if true, could undermine the argument above?
3. The argument would be least persuasive if which of the following were found to be true?

Step 4:  Read the stimulus and mark the evidence/premises as E/P and conclusion as C

Note :
Quickly glance through the first and last sentence in an argument. 90%
of the time the conclusion will be the first or last sentence. You
don't have to note down the entire sentence in your scratch paper .
Paraphrase the sentence or use the same sentence if it is not too long.

In this argument the last sentence is the conclusion and the remaining sentences are premises.

Step 5 : Find the assumption that connects the premises to the conclusion

Central Assumption : The wild animals would not get entangled in the discarded rings during the three day period after which the plastic would be disintegrated.

Other Assumption : The plastic would be exposed to sunlight

Step 6 : Eliminate answer choices that doesn't weaken the central assumption

(A) The switchover to the new plastic rings will take at least two more years to complete. Irrelevant to the central assumption : Eliminate


(B) After the beverage companies have switched over to the new plastic
rings, a substantial number of the old plastic rings will persist in
most aquatic and woodland environments.

Weakens the argument : Note woodland environment correlates with the habitat of wild animals : Keep It


(C) The new plastic rings are slightly less expensive than the old rings.

Irrelevant to the characteristics of plastic rings : Eliminate


(D) The new plastic rings rarely disintegrate during shipping of
beverage six-packs because most trucks that transport canned beverages
protect their cargo from sunlight.

The premises are related to rings that are abandoned not transported . Eliminate


(E) The new plastic rings disintegrate into substances that are harmful
to aquatic animals when ingested in substantial quantities by them.

Since the argument focuses on wild animals and not aquatic animals : Irrelevant to the premises:  Eliminate


So the correct answer is B


Recommended Books

1) The PowerScore GMAT Critical Reasoning Bible: A Comprehensive System for Attacking the GMAT Critical Reasoning Questions

2) Critical Reasoning GMAT Preparation Guide, 4th Edition (Manhattan GMAT Preparation Guides)

3) Kaplan GMAT Verbal Workbook

4) Critical Reasoning & Reading Comprehension GMAT Preparation Guide (Manhattan Gmat Prep)