The Rotation Curve of a Galaxy Is a Graph Showing

The rotation curve of a galaxy is a graph showing the galaxy's speed of rotation at different distances from the center.The observed rotation curve in the outer parts of a typical large spiral galaxy

A) decreases suddenly to zero at the outer edge of the visible galaxy.
B) decreases smoothly with increasing distance from the center,following a Keplerian curve.
C) is quite flat (roughly the same speed at all distances) .
D) increases drastically with increasing distance from the center,as shown by the spiral arms.