The Tujia dog is a small hairless beast that lives only in the southern United States. Before humans settled in the southern United States, Tujia's natural enemies were not strong, so Tujia prospered in the southern United States. When humans began to hunt them, Tujia dogs became extinct Therefore, it must be that people's minefields have caused its extinction. Which of the following, if true, has most severely weakened the reasoning above? ['While humans settled in the southern United States, they also brought new species that may be natural enemies of Tujia dogs.', 'Since the first humans settled in the southern United States, Tujia dogs have remained in some parts of the southern United States for about 300 years.', 'Some breeds of Tujia dogs run faster than leopards.', 'In the southern United States people hunt another mammal that is easily preyed by natural enemies but has never been extinct.']