Which statement is true about kilwa and aksum?

a. they were christian kingdoms.
b. they were muslim kingdoms.
c. they were city-states on the coast.
d. they grew powerful through trade.

crop rotation kepy different plants in the soil instead of once constintly. when switching out plants you have different nutrients being absorbed at different speeds and different roots growing differently therfore the spoil and water flow have to adapt and carry fresh nutrients to carry the constant changes that were going on in the soil.

it refers to race, i am pretty sure this was a popular term in nazi germany or something.