Researcher: This fall I returned to a research site to recover the armadillos I had tagged there the previous spring. Since a large majority of the armadillos I recaptured were found within a few hundred yards of the location of their tagging last spring, I concluded that armadillos do not move rapidly into new territories. Which one of the following is an assumption required by the researcher's argument? ['A large majority of the recaptured armadillos did not move to a new territory in the intervening summer and then move back to the old territory by the fall.', 'Predators did not kill any of the armadillos that had been tagged the previous spring.', 'The tags identifying the armadillos cannot be removed by the armadillos, either by accident or deliberately.', 'Of the armadillos living in the area of the tagging site last spring, few were able to avoid being tagged by the researcher.']