Here are my 2 cents...
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?
I've highlighted the pieces separately to draw attention to the role each piece plays independently.
The word
result, as we know, signals the conclusion. This can be deciphered even if you are the kind of person that does not read the question first.
If you have read the question before the passage you know that
say local ecologists in the passage clearly correlates with the question, telling you exactly where the conclusion lies. You would be able to decipher this even if you missed the word
result.
That said, the conclusion follows. Pay attention to the words; they say
solely stemming from the blackening of the woods. This means there is no reason why red-brown earthworms would dwindle.
Now you need to find the choice that strengthens this idea, that is, while favoring both types of what could contribute to the rise in black earthworm population?
The former part of the passage already states that black earthworms could not be well disguised and hence often fell prey to predatory birds. So what could be helping their proliferation now? Blackening of the woods. What can strengthen this position? Eliminate the choices that suggest the red-brown earthworms are dwindling.
A) The number of red-brown earthworms in the Millerton woods has steadily dropped since the factory began operations.
This is a weakening idea. Plus it could go contrary to what the passage suggests.B) The birds that prey on earthworms prefer black worms to red-brown worms.
This may be close, so I would keep itC) Climate conditions since 1990 have been more favorable to the survival of the red-brown worm than to the black worm.
This option clearly strengthens the conclusion. Although I would say choice B goes with the tide, it does not to anything to strengthen the conclusion. Now we don't want a choice that simply states the lines in the passage again. This choice states that even though climatic conditions favored the red-brown worms, the black worms were able to proliferate. Why? Because the woods blackened and the birds were not able to prey on the worms.D) The average life span of the earthworms has remained the same since the factory began operations.
E) Since the factory took steps to reduce emissions six months ago, there has been a slight increase in the earthworm population.
Irrelevant choices. _________________