What Was the Climatic Change That Affected the Distribution of Peoples

What was the climatic change that affected the distribution of peoples in Africa?

A) The entire continent became progressively wetter due to annual increases in rainfall beginning in the 3rd millennium B.C.E.
B) Increased rainfall produced widespread rain forests that stretched across Africa from the Atlantic coastline to Ethiopia.
C) A decrease in annual rainfall turned the northern areas of the continent into the Sahara desert by 3000 B.C.E.
D) A decrease in annual rainfall destroyed all of the Paleolithic rain forests of Africa and created widespread savannas, particularly in west Africa.