$\mathrm{AB}$ is a chord of the circle $\mathrm{x}^{2}+\mathrm{y}^{2}-4 \mathrm{x}-2 \mathrm{y}+1=0$ subtending a right angle at the centre. Then the locus of the centroid of the triangle PAB, where $\mathrm{P}$ moves on the circle is
(a) a parabola
(b) an ellipse
(c) a hyperbola
(d) a circle