Archaeologist: After the last ice age, groups of paleohumans left Siberia and crossed the Bering land bridge, which no longer exists, into North America. Archaeologists have discovered in Siberia a cache of Clovis points -- the distinctive stone spear points made by paleohumans. This shows that, contrary to previous belief, the Clovis point was not invented in North America. Which one of the following, if true, would most strengthen the archaeologist's argument? ['Archaeologists have discovered in Siberia artifacts that date from after the time paleohumans left Siberia.', 'The Clovis points found in Siberia are older than any of those that have been found in North America.', 'Clovis points were more effective hunting weapons than earlier spear points had been.', 'Some paleohuman groups that migrated from Siberia to North America via the Bering land bridge eventually returned to Siberia.']