GRE数学解析(2)

　　P, Q, and R are three points in a plane, and R does not lie on line PQ. Which of the following is true about the set of all points in the plane that are the same distance from all three points?

　　A. It contains no points.

　　B. It contains one point.

　　C. It contains two points.

　　D. It is a line.

　　E. It is a circle.

　　思考ING...