During the 19th century, the powerful nations of Europe "carved up" Africa into colonies and territories. Before colonization, how were the borders in Africa established? Select one:

a.
Borders were formed by rivers, mountains and other geographic features.

b.
Borders were determined by allegiance to a central leader or a community.

c.
Borders were maintained by military leaders who worked to separate religious groups.

d.
Borders generally did not exist before the colonization of Africa.