Conclusion: the environmentalists' claim that pollution is eliminating many amphibian species every year is undermined.
Why? Last year biologists learned that there are many more species of amphibians in existence than they had previously known.
Alright, so what's the issue? Well, just because there are more species that previously thought does not mean that pollution is not eliminating many of these species every year.
For example, even if we find a different genus of panda, that doesn't mean that the panda is not an endangered animal.
This is exactly what answer choice (E) is describing: just because biologists now know there are more species than previously thought, i.e. there is a change in their knowledge of objects (there are more of them than previously thought), does not mean that their claim that pollution is eliminating many of these species every year is wrong, i.e. changes in the objects themselves (that pollution is eliminating many of these objects every year).
Answer choice (D) is not correct because the argument does not describe a correlation between two phenomena. We merely are told that there are more species than were once believed. There is not correlation/causation flaw in the argument.
Hope that clears things up! Please let us know if you have any other questions.
