The locus of the midpoint of a line segment that is drawn from a given external point P to a given circle with center O and radius r, is:
<spanclass=′latex−bold′>(A)</span>a straight line perpendicular to PO<spanclass=′latex−bold′>(B)</span>a straight line parallel to PO<spanclass=′latex−bold′>(C)</span>a circle with center P and radius r<spanclass=′latex−bold′>(D)</span>a circle with center at the midpoint of PO and radius 2r<spanclass=′latex−bold′>(E)</span>a circle with center at the midpoint PO and radius 21r