What Was One of the Methods the Inca Leaders Used

What was one of the methods the Inca leaders used to help maintain control of those they conquered?

A) By making the conquered people move to unfamiliar areas.
B) By taxing them heavily to keep them poor and dependent on the Inca.
C) By placing military forces over them to enforce obedience.
D) Forcing them to serve in large numbers in military service from the Inca.
E) Using spies to help stamp out all resistance before it could get a strong foothold.