The Object of Introducing a Transition Curve at Each End

The object of introducing a transition curve at each end of the circular curve is

A) to obtain a gradual increase of curvature from zero at the tangent point to the specified quantity at the junction of the transition curve with the circular curve
B) to provide a satisfactory means of obtaining a gradual increase of super-elevation from zero on the tangent point to the specified amount on the main circular curve
C) to accomplish gradually the transition from the tangent to the circular curve and from the circular curve to the tangent
D) all of the above