What is the key difference between compound curves and reverse curves?$(2$ points$)$

a$.$ Compound curves consist of two consecutive curves of different radii, while reverse curves consist of curves with the same radii.

b$.$ Compound curves have their centres of curvature on the same sids of the common tangent point, while reverse curves have their centres on opposite sides. I

c$.$ Compound curves are used to avoid obstacles, while reverse cury are used to minimize forces at the common tangent point.

d$.$ None of the above