The cypress trees of the Louisiana wetlands are threatened by the exploding population of nutria, a type of South American rodent introduced into the area in the 1930s in hopes of starting a nutria fur industry. Unfortunately, no one wanted the fur, and now the rodents number in the millions. A park ranger has suggested introducing the South American jaguar, the nutria’s natural predator, into the Louisiana wetlands as a way to control the nutria population. Which of the following, if true, casts the most doubt on the ranger’s plan to introduce jaguars as an effective way to control the nutria population ？（）
A. Past attempts to control the nutria population through traps and poison have resulted in limited and temporary population reductions.
B. A program in Florida found that the best way to conserve the root systems of wetland trees such as cypresses is to surround the trees’ roots with tough plastic barriers.
C. The jaguar is a large and deadly predator that, if introduced, could kill livestock, pets, or even humans that it encounters in the Louisiana wetlands.
D. During the past year an unusually cold winter killed an estimated 35 percent of the nutria population in the Louisiana wetlands.
E. The South American jaguar is a predator of the ferret, which is currently the chief predator of the nutria in the Louisiana wetlands.
