In the last year, biologists have learned that there are many

Powerscore explanation:

Flaw in the Reasoning. The correct answer choice is (E)

This stimulus begins with the fact that over the past year, it has been discovered that there a lot more species of amphibians than had been thought. The author asserts that this premise weakens the environmentalist claim that each year, many amphibian species are killed by pollution:

Premise: Environmentalists claim that many species of amphibians die each year as a result of pollution.

Premise: Over the past year, however, scientists have discovered that there are more amphibian species in existence that had been previously thought.

Conclusion: Thus, the environmentalist claim is undermined.
The problem with this argument is that one does not preclude the other in any way; regardless of the big recent discoveries, pollution could certainly be killing many amphibian species each year. As you might have seen coming, the stimulus in this case is followed by a Flaw question, so the correct answer choice should describe the misunderstanding reflected in the author’s reasoning.

Answer choice (A): This choice describes confusion between categories and those things that are categorized. This does not describe the issue with the author’s reasoning, so it should be ruled out of contention.

Answer choice (B): This choice describes the classic conditional error of Mistaken Reversal—mistaking a necessary condition for a sufficient one. The stimulus’ flaw, however, is not a conditional reasoning error, so this cannot be the correct answer choice.

Answer choice (C): The author’s argument is based on a misunderstanding of the numbers, rather than something to do with cause and effect. Since the argumentation is not based on causal reasoning, this cannot be the choice that describes the flaw.

Answer choice (D): This choice, like incorrect answer choice (C), describes a causal reasoning flaw. The author’s argument, however, is not based on causal reasoning, so this choice does not describe the flaw.

Answer choice (E): This is the correct answer choice. We now know about many more amphibian species, but clearly that doesn’t mean that the number that exists hasn’t continued to dwindle.