Rabbits were introduced to Numa Island in the nineteenth century. Overgrazing by the enormous population of rabbits now menaces the island' s agriculture. The government proposes to reduce the population by using a virus that has caused devastating epidemics in rabbit populations elsewhere. There is, however, a chance that the virus will infect the bilby, an endangered native marsupial. The government' s plan, ttherefore, may serve the interests of agriculture but will clearly increase the threat to native wildlife. Which of the following, if true, most seriously weakens the argument? ['There are no species of animals on the island that prey on the rabbits.', 'The virus that the government proposes to use has been successfully used elsewhere to control populations of rabbits.', 'Overgrazing by rabbits endangers many of the plants on which bilbies feed.', 'There is no alternative means of reducing the rabbit population that would involve no threat to the bilby.']