I believe it is B native Americans shifted from hunting and gathering to acquiring animal hides for trade. Because of process of elimination:
not A because natives did use European technology such as guns, and adapted to using horses and other livestock
not C because natives did not adapt European customs, just the items they received during the Columbian Exchange (not a cultural exchange)
not D because natives died as a result of European diseases, therefore the Europeans did not aid in curing those diseases but rather caused them