In the last year, biologists have learned that there are many more species of amphibians in existence than had previously been known. This definitely undermines environmentalists' claim that pollution is eliminating many of these species every year. The reasoning in the argument above is most vulnerable to criticism on the grounds that it involves a confusion between ['a correlation between two phenomena and a causal relationship between them', 'changes in our knowledge of objects and changes in the objects themselves', 'a cause and an effect', 'a condition necessary for a phenomenon and one that is sufficient for it']