Why Did the Native American Population in Texas Decline in the Centuries

Why did the Native American population in Texas decline in the centuries following European colonization?

A) Europeans paid native peoples for their land and encouraged them to leave the area.
B) Marriage between native peoples and European settlers quickly diffused the native population.
C) Native American tribes wiped each other out fighting over land unclaimed by European settlers.
D) Nothing in particular contributed to the decline of the Native American population.
E) Diseases decimated native communities and violence between native peoples and Europeans was frequent.