The following is a letter to the editor of an environmental magazine.
"In 1975 a wildlife census found that there were seven species of amphibians in Xanadu National Park, with abundant numbers of each species. However, in 2002 only four species of amphibians were observed in the park, and the numbers of each species were drastically reduced. There has been a substantial decline in the numbers of amphibians worldwide, and global pollution of water and air is clearly implicated. The decline of amphibians in Xanadu National Park, however, almost certainly has a different cause: in 1975, trout—which are known to eat amphibian eggs—were introduced into the park."
Write a response in which you discuss what specific evidence is needed to evaluate the argument and explain how the evidence would weaken or strengthen the argument.