A.The Roman empire relied on physical features as natural barriers.
Put simply, the difference between a unitary and a federal government is that a unitary government puts its power in one central government while in a federal system the governing power is divided into federal and local governing bodies that connect to the national government.
Answer: Parallax
Explanation: Parallax is usually an error which should be avoided when taking measurements. It is the observed difference in the apparent position of an object when viewed from different positions. Motion parallax is the change in the position of an object due to the viewer's movement. In motion parallax, the object distance to the observer's eye seems to affect the relative motion of the object. That is objects close by or near the observer's eye such as mile markers seems to rush or whiz past relative to the observer's direction while distant objects such as hills and mountain tops moves relatively slowly in the opposite direction.
Over a life time of an individual intelligence tends to increase. You learn more things that will have more value then the things you learned earlier in life.
I believe it is c they were ruled by emperors
