Which of the Following Was a Major Factor in the Success

Which of the following was a major factor in the success of Muslim invaders of North Africa?

A) The North Africans had already adopted Islam and begun to write in Arabic.
B) The North African tribes were not unified and distrusted each other.
C) The North African tribes were pacifist and would not fight back.
D) The North Africans were worn down by years of fighting with the Christians.