B. incenter
The incenter is the point on the interior of the triangle that is equidistant from all sides. Since a point interior to an angle that is equidistant from the two sides lies on the angle bisector, then the incenter must be on the angle bisector of each angle of the triangle.
The incenter will be the center of an inscribed circle because it is equidistant from all three sides, hence the equal radii of the inscribed circle.
Circumcenter, on the other hand, is used to find the center of a CIRCUMSCRIBED circle around the triangle touching all three vertices.