Two different dates have been offered as the approximate end point of the last ice age in North America. The first date was established by testing insect fragments found in samples of sediments to determine when warmth-adapted open-ground beetles replaced cold-adapted arctic beetles. The second date was established by testing pollen grains in those same samples to determine when ice masses yielded to spruce forests. The first date is more than 500 years earlier than the second. The statements above, if true, most strongly support which one of the following conclusions about the last ice age and its aftermath in North America? ['Ice masses continued to advance through North America for several hundred years after the end of the ice age.', 'Toward the end of the ice age, warmth-adapted open-ground beetles ceased to inhabit areas where the predominant tree cover consisted of spruce forests.', 'Among those sediments deposited toward the end of the ice age, those found to contain cold-adapted arctic beetle fragments can also be expected to contain spruce-pollen grains.', 'Toward the end of the ice age, warmth-adapted open-ground beetles colonized the new terrain opened to them faster than soil changes and seed dispersion established new spruce forests.']