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