Two Types of Earthworm, One Black and One Red-Brown, Inhabit the Woods GMAT Critical Reasoning

Question: Two types of earthworm, one black and one red-brown, inhabit the woods near the town of Millerton. Because the red-brown worm's coloring affords it better camouflage from predatory birds, its population in 1980 was approximately five times that of the black worm. In 1990, a factory was built in Millerton and emissions from the factory blackened much of the woods. The population of black earthworms is now almost equal to that of the red-brown earthworm, a result, say local ecologists, solely stemming from the blackening of the woods.

Which of the following, if true, would most strengthen the conclusion of the local ecologists?

1. The number of red-brown earthworms in the Millerton woods has steadily dropped since the factory began operations.
2. The birds that prey on earthworms prefer black worms to red-brown worms.
3. Climate conditions since 1990 have been more favorable to the survival of the red-brown worm than to the black worm.
4. The average life span of the earthworms has remained the same since the factory began operations.
5. Since the factory took steps to reduce emissions six months ago, there has been a slight increase in the earthworm population.

‘Two types of earthworm, one black and one red-brown, inhabit the woods near the town of Millerton.’ – is a GMAT critical reasoning topic. This GMAT Critical Reasoning topic has been taken from the book ‘Manhattan prep GMAT Critical Reasoning 6th Edition’. In this particular topic, candidates are asked to select the option that strengthen the conclusion of the local ecologists. In this question, the candidates need to provide an option that strengthen the conclusion of the local ecologists provided in the passage. 

The GMAT critical reasoning tests the logical and analytical skills of the candidates. Critical reasoning in GMAT requires candidates to find the argument's strengths and weaknesses or the logical flaw in the argument.  The GMAT CR section contains 10 -13 GMAT critical reasoning questions out of 36 GMAT verbal questions.

Answer: C
Explanation: Question Type: Strengthen/Weaken the Argument

In this GMAT critical reasoning question type, candidates need to strengthen an argument by providing a piece of supportive evidence or statement. By answering the GMAT critical reasoning questions by studying the argument of the passage can simplify the understanding. Then the options are supposed to be check to find the perfect piece of evidence to support it.

The passage implies that one of the options is most strengthening the conclusion of the local ecologists'

Option A :The number of red-brown earthworms in the Millerton woods has steadily dropped since the factory began operations.
-Option A is not sufficient because it states about the red-brown earthworms that decreased by themselves.

Option B :The birds that prey on earthworms prefer black worms to red-brown worms.
-Option B states that birds prefer worms. They prefer black worms to red worms. We can understand from this that the blackening of the woods does not play any role to help black worms. Hence option B is not sufficient.

Option C :Climate conditions since 1990 have been more favorable to the survival of the red-brown worm than to the black worm.
-Option C states that red worms do not decrease but red worms increased more than in 1980. The blackening of the woods plays an important role to help worms. Hence option C is the correct answer.

Option D:The average life span of the earthworms has remained the same since the factory began operations.
-Option D implies the average life span of earthworms changes. Hence option D is incorrect.

Option E :Since the factory took steps to reduce emissions six months ago, there has been a slight increase in the earthworm population.
-Option E states that the factory reduces emissions. This increases the woods to get blackened, leading to an increase in earthworms. The blackening of the woods does not play any role. Hence option E is incorrect.