For a parabola if
a) Squared term is x
Parabola either opens up or down.
Positive coefficient means upward opening and negative coefficient means downward opening
b) Squared term is y
Parabola either opens right or left
Positive coefficient means rightwards opening and negative coefficient means leftwards opening
The given parabola opens upward, this means squared term is x with positive co-efficient.
So the correct answer to this question is option D