The black codes
what were the black codes based on?

The Black Codes were laws passed in 1865 and 1866 by Southern states in the United States after the American Civil War in order to restrict African Americans' freedom, and to compel them to work in a labor economy based on low wages or debt.

the answer would be:

b. race

geography

this is because warmer climates often don't get people sick from the flu and regions where it was often colder more people received the flu. hope this if you need more reasoning i am here to