Please answer these two questions in order :) What is the meaning of "Oral Tradition"?
Choose one of the following
a. The use of spoken language to tell history
b. The act of talking frequently
c. The act of writing things down after hearing them
d. The use of spoken words in the long past (not today)

“European countries that carved up Africa to add to their overseas empires had their own reasons for setting colonial borders where they did. They did not consider the borders of the different ethnic groups of the Africans who already lived on the land they colonized. As a result, the European colonies in Africa contained populations that were ethnically diverse. When African countries declared independence, the new national borders closely followed the old colonial borders, preserving that diversity. Establishing a sense of national unity is difficult, however. Many people have a stronger identification with their ethnic group than with the country they live in. For example, the Hausa are citizens of Nigeria, but many feel closer ties to the people and culture of the Hausa than to the country of Nigeria.

Another factor working against national unity is that a West African ethnic group does not typically live in only one country. Some Yoruba people, for example, live in Nigeria. Other Yoruba live in Benin. No matter where they live, the Yoruba feel a closer connection to other Yoruba people than to Nigeria or Benin.” —Discovering World Geography

According to the passage, national unity is a problem in Africa. What are two causes for this? Please support your answer with evidence from the passage.