Read the Following Scenario and Answer the Question Below

Read the following scenario and answer the question below.
In the early years of the 20th century there were lush stands of tall grasses in the valley on the east side of the Chiricahua Mountains in Arizona, stretching to Mexico on the south and New Mexico on the east. Dramatic summer rainstorms dumped huge amounts of water, very quickly, on the rocky upper slopes. The water ran down the slopes and into the grasslands, where it quickly soaked into the soft, porous soil where prairie dogs were active. Cattle ranching was in full swing, utilizing the rich grasses, but the ranchers did not appreciate the multitudes of prairie dogs that lived in the grasslands. Prairie dogs constantly dig through soil, making new burrows and eating grasses, roots and all. It was commonly believed that cattle would stumble in the prairie dog holes, break legs, and die of starvation. In addition, many ranchers were convinced that the prairie dogs would destroy the grasses because they directly competed with the cattle for food. The ranchers had already done away with most predators that might possibly affect cattle, and now they turned their attention to the prairie dogs. The ranchers became a part of a new federally sponsored movement to poison the grassland prairie dogs. This movement took root and spread through the 1920s and 1930s.
-One of the conclusions that can be drawn from this scenario is that _______________

A) predators were unimportant components of this ecosystem; their removal caused no subsequent problems.
B) once humans change one thing in an ecosystem, they may find unexpected results occurring elsewhere in the ecosystem.
C) prairie dogs were unimportant components of this ecosystem; their removal caused no subsequent problems.
D) prairie dogs were part of a negative feedback loop once they were removed.
E) cattle improved the soils, contributing to this ecosystem.