Angle bisectors of a parallelogram form a _____.

Angular bisectors from A and B intersect at P, B and D intersect at Q, C and D intersect at R, and A and C intersect at S.
In a parallelogram ABCD, AC is parallel to BD.
$$\angle\ CAB\ +\angle\ ACD\ =\ 180^{\circ\ }$$
$$\angle\ CAS\ +\angle\ ACS\ =\ 90^{\circ\ }$$
In triangle CAS,
$$\angle\ ASC\ =\ 180^{\circ\ }-90^{\circ\ }=90^{\circ\ }$$
As all the angles of PQRS are $$90^{\circ\ }$$, PQRS is a rectangle.

Answer is option D.