49. The author's argument that destroying bot-flies and mosquitoes would be a beneficial action is most weakened by all of the following except_______ (A) parasites have an important role to play in the regulation of populations (B) the elimination of any species can have unpredictable effects on the balance of nature (C) the pests themselves are part of the food chain (D) these insects have been introduced to the area by human activities (E) elimination of these insects would require the use of insecticides that kill a wide range of insects