What is probably the primary reason why historians might have trouble with studying medieval african cultures and history?

select the best answer from the choices provided.
nobody has yet translated the great works of african history into a language spoken today.
it is a very complicated history with many different states and nations overlapping each other.
all of their records were destroyed when europeans came to colonize africa in later years.
much of african history is orally based, retold by word of mouth, so historians must rely heavily on artifacts and items found.