When Climatic Change Began to Create the Sahara Desert as We

When climatic change began to create the Sahara Desert as we know it today,

A) farmers moved south into the Niger River valley where they could continue familiar ways.
B) Saharan herders migrated eastward, where they found lands conducive to their way of life.
C) many of the pastoral herders became nomadic, using the scant resources of the desert to eke out a living.
D) agriculture spread south into the rain forests, where cereals began to be grown for the first time.
E) the cultivation of millet and rice was carried into both the Niger and Nile River valleys by those forced to migrate.