In my opinion I think it would be C:Social organizations because when your social you learn new things.
You forgot to put the answer choices
Congress did not have the authority it prohibit slavery in the territories
The Kingdom of Aksum became a center-point for Christianity in Africa and they were the first country to use crosses on their coins. If it weren't for them, the Eritrean and Ethiopian Orthodox Churches wouldn't have developed. This conversion to Christianity occurred under emperor Ezana.
I believe the answer is D. The lack of water in the north prevents settlement in the area.