The Main Advantage of Providing Transition Curves on Highways, Is

The main advantage of providing transition curves on highways, is

A) to obtain transition from the tangent to the circular curve and from the obtain transition from the tangent to the circular curve and from the circular to the tangent
B) to obtain a gradual increase of curfature from a value of zero at the tangent to a maximum at the circular curve
C) to have a gradual increase of super-elevation from zero at the tangent to a specific maximum at the circular curve
D) all of the above