What did copernicus argue concerning the construction of the universe

Which factor contributed to the rise of african empires such as ghana and mali?

What do you know about harriet tubman?

Using mr smith and his id, identify two potential internal validity threats that might affect the a—b design. tell me how that threat might impact conclusions in the a—b design. note #1: you cannot use maturation (since i already did that one for note #2: there are some mr smith id threats that won’t have much impact in a single case design.