Which of these longstanding african developments ended in the 1500s?

a. the spread of islam in africa

b. conversion to christianity

c. the bantu migrations

d. the spread of farming?

Islam continues to grow in Africa to this day. Christian mission work continues in Africa too. And farming continues to expand.

The Bantu migrations ended in the 1500s. Bantu-speaking peoples migrated from Western Africa (in the area of modern Nigeria) throughout southern parts of Africa starting around 1000 BC and continuing to the 1500s (or perhaps a bit later, by some accounts).