By the Time Europeans Had Begun Serious Exploration and Settlement

By the time Europeans had begun serious exploration and settlement of the Northeast,

A) native Americans were already fully aware of the dangers Europeans posed to their civilizations.
B) most tribes were already too weakened by disease to offer any resistance.
C) economic and cultural changes among Woodland Indians had produced two opposing tribal alliances.
D) the social and political unity among Woodland Indians had already been broken.