All of the Following Make It Difficult for Modern Archaeologists

All of the following make it difficult for modern archaeologists to study the earliest people in North America except that __________________.

A) early Native American populations were small and carried relatively few material possessions
B) only a small number of significant sites ever existed and were spread over the entire North American continent
C) all of the earliest sites have already been found and there is nothing left for modern archaeologists to study
D) areas of the Pacific Coast where migrations may have occurred are now below sea level