ANSWER ASAP PLEASE Who replaced slaves in Europe during the Middle Ages?

A: artisans
B:Clergy
C:Knights
D:Serfs

How does the supremacy clause of the u.s. constitution affect the states? o a. it requires each state to establish a supreme court. b. it declares that the federal government can take away state powers if necessary. o c. it allows state governments to overthrow the federal government if necessary. o d. it ensures that the u.s. constitution overrules each state constitution