the answer is D, (0,-3), (0,3).
The vertices are the highest and lowest points of each parabola of the graph. On a positive parabola (one that curves upward), the vertice is the lowest point, on a negative parabola (one that curves downward), the vertice is the highest point. In this particular case, the vertice of the parabola on top is (0,3) because its lowest point is (0,3). The vertice of the parabola on the bottom is (0,-3) because its highest point is (0,-3).