HOw to find curve? I don't understand how this is wrong. I tried AF and OC. Either of those should be right, since those depict 45 angles. What's the problem?

You are not asked the position, you are asked about the velocity in the vertical direction. The horizontal axis of the graph is time. Since only gravity is acting in the vertical direction $v_y(t)=v_y(0)-gt$. Therefore the graph is linear in time, with a negative slope. So the answer is AE