Why were african colonies so profitable to european imperialist powers?

a)they did not pay for the land or its resources, and labor was either free or extremely cheap.
b)the demand for cultural products from africa was incredibly high in europe.
c)native africans did not understand the value of their natural resources, and sold them cheap.
d)raw materials were easily shipped to africa from the american colonies.

a) They did not pay for the land or its resources, and labor was free or extremely cheap.

Explanation:

The European colonization of Africa has left grave consequences on this continent. Population exploitation was widespread across Africa. Europeans called it hired labor, and in fact, it was the forced labor of the hardest physical job. They used African resources as private property. A considerable number of people have suffered in Africa as a result of hard physical work.

For example, over 20,000 natives lost their lives during the construction of the Congo railway, which lasted for ten years.European factors pressured tribal leaders to force them to choose the most active individuals to work eventually. World War I weakened Europe economically. Africans also felt these consequences. After World War I, the situation got worse. A labor tax on Africans was introduced. To pay him, they were forced to work for Europeans.

d.he wanted to send diplomats to communist countries.