Excavations of the Roman city of Sepphoris have uncovered numerous detailed mosaics depicting several readily identifiable animal species: a hare, a partridge, and various Mediterranean fish. Oddly, most of the species represented did not live in the Sepphoris region when these mosaics were created. Since identical motifs appear in mosaics found in other Roman cities, however, the mosaics of Sepphoris were very likely created by traveling artisans from some other part of the Roman Empire. Which of the following is an assumption on which the argument depends? ['No motifs appear in the Sepphoris mosaics that do not also appear in the mosaics of some other Roman city.', 'There was not a common repertory of mosaic designs with which artisans who lived in various parts of the Roman Empire were familiar.', 'All of the animal figures in the Sepphoris mosaics are readily identifiable as representations of known species.', 'There is no single region to which all the species depicted in the Sepphoris mosaics are native.']