The author of the passage implies that, in what is now the United States, archaeological evidence of inhabitation in the period from 40,000 to 25,000 years ago is lacking because that region A. had its oldest habitation sites inundated following a postglacial rise in sea level. B. had many resource-rich rivers that facilitated the dispersal of early inhabitants from an initial concentration in coastal areas. C. was sparsely populated until about 25,000 years ago. D. was colonized less than 25,000 years ago. E. was inhabited only by hunter-gatherers until 25,000 years ago.