a. Since a line doesn't have endpoint, it doesn't matter which
two points we use to name a line so we could call this line DC.
b. A ray is a figure that starts at and endpoint and continues
forever in one single direction. So a ray here would be ray AB.
c. Opposite rays are two rays that share a common endpoint,
have no other points of intersection, and all points are collinear.
So ray EC and ray ED would be opposite rays.