Biologists often announce that a certain kind of animal has been found capable of using tools; this usually refers to something like using a stick to hunt for ants in a log, or a stone to crack nuts. But such announcements are completely unsurprising, since all animals use tools. Birds build nests, fish hide in the mud to escape predators, and squirrels use buildings as shortcuts between trees. If an animal executes its purpose by means of an external physical object, then that object can reasonably be regarded as a tool. Which one of the following most accurately describes the role played in the argument by the claim that the biologists' announcements that a certain animal has been found capable of using tools are unsurprising? ['It addresses a weakness in the biologists\' announcements that stems from their ambiguous use of the word "external. "', "It provides evidence that the animals' activities given as examples are purposeful.", 'It is the conclusion of the argument.', "It calls into question the basis of the biologists' conception of a tool."]