The authors argument that destroying bot-flies and mosquitoes would be a beneficial action is most weakened by all of the following except

The correct option is D these insects have been introduced to the area by human activities
The passage states of how man can be beneficial, by killing of pests and other things that destroy wildlife. But in the last line, it is given that 'But, except in cases where the experiment has proved his intervention to be beneficial, the less he upsets the balance of Nature the better, even when he tries to be an earthly Providence'.This is given in option D which speaks of human intervention.