Opposite vertices A(2,3) and C(8,5) of a quadrilateral ABCD are given. The diagonals intersect at O(5,4). If vertex B is at (6,9), which of the following are the coordinates of vertex D so that ABCD is a parallelogram?
(a) (5,4)
(b) (7,14)
(c) (4,−1)
(d) (12,11)