Currents within the mantle cause the earth's plates to move and shift s molten material rises and falls due to density and gravity
Conduction
Radiation
Wind
Convection

a is correct

hope this let me know if it is right

hi!

your correct answer would be a

~courtney

explanation:

the addition to geographic boundaries that might have  kept the people of the huang river civilization from traveling to far distance region is that they had learned about the other river valley civilizations but feared contact would bring invasion.

hope this .

plz give me brainliest!