Which of these is the best definition of an ellipse?
A. The set of all points in a plane that are a certain distance from a
single point
B. The set of all points in a plane for which the difference between
the distances to two fixed points equals a certain constant
C. The set of all points in a plane for which the sum of the distances
to two fixed points equals a certain constant
D. The set of all points in a plane that are equidistant from a single
point and a line