Naturalist: The recent claims that the Tasmanian tiger is not extinct are false. The Tasmanian tiger' s natural habitat was taken over by sheep farming decades ago, resulting in the animal' s systematic elimination from the area. Since then naturalists working in the region have discovered no hard evidence of its survival, such as carcasses or tracks. In spite of alleged sightings of the animal, the Tasmanian tiger no longer exists. Which one of the following is an assumption on which the naturalist's argument depends? ['Those who have reported sightings of the Tasmanian tiger are not experienced naturalists.', "Every naturalist working in the Tasmanian tiger's natural habitat has looked systematically for evidence of the tiger's survival.", 'Some scavengers in Tasmania are capable of destroying tiger carcasses without a trace.', 'The Tasmanian tiger did not move and adapt to a different region in response to the loss of habitat.']