Given:
The graph of a parabola.
To find:
The equation of the parabola.
Solution:
From the given graph, it is clear that the vertex of the parabola is at point (0,0) and it is a horizontal parabola.
The general equation of a horizontal parabola is:

Where, a is a constant.
If a<0, then the parabola opens left and if a>0, then the parabola opens right.
Equations in options B and D are of the form
but a<0 in option B and a>0 in option D.
In the given graph the parabola opens right, so the value of a mus be a positive number. So, the required equation is:

Therefore, the correct option is D.