Neighboring landholders: Air pollution from the giant aluminum refinery that has been build next to our land is killing our plants.
Company spokesperson: The refinery is not to blame, since our study shows that the damage is due to insects and fungi.
Which of the following, if true, most seriously weakens the conclusion drawn by the company spokesperson?
(A) The study did not measure the quality of pollutants emitted into the surrounding air by the aluminum refinery .
(B) The neighboring landholders have made no change in the way they take care of their plants.
(C) Air pollution from the refinery has changed the chemical balance in the plants’ environment, allowing the harmful insects and fungi to thrive.
(D) Pollutants that are invisible and odorless are emitted into the surrounding air by the refinery.
(E) The various species of insects and fungi mentioned in the study have been occasionally found in the locality during the past hundred years.
The accusation of the landholders is that air pollution from the aluminum refinery is responsible for the damage to their plants.
The refinery’s spokesperson admits that the plants of the neighboring landlords are getting damaged, but says that the studies undertaken by the refinery found that the damage to the plants was, in fact, being caused by insects and fungi. He therefore concludes that air pollution from the refinery is not responsible for the damage to the plants.
We have been asked to spot the argument which would weaken the spokesperson’s conclusion.
Obviously, his conclusion would be most weakened if it is found that the growth of insects and fungi in the area was itself facilitated by the air pollution caused by the refinery.
In this case, it is the refinery which would be indirectly, even if not directly, responsible for the damage to the plants. This is what is stated in (C), which is the answer.
It is easy to see that none of the other choices logically connects (a) air pollution by the refinery, (b) growth of insects and fungi, and (c) damage to the plants.
(In this example, all the four wrong choices are irrelevant to the conclusion in the passage.)