Concept:The northern boundary of Africa is determined by the body of water separating it from Europe.Explanation:Africa is bordered to the north by the Mediterranean Sea.This sea lies between Africa and Europe.The Atlantic Ocean is found to the west and south-west of Africa.The Red Sea lies to the north-east of Africa.The Indian Ocean is located to the east and south-east of Africa.Therefore, only the Mediterranean Sea forms the northern boundary.Answer:A. Mediterranean Sea