Since the squared term is x the parabola can either open or down. If the square was on y term, the parabola would have open right or left.
The sign of the leading term determines the direction of opening. If leading term is positive and squared term is x, the parabola opens up and if the leading term is negative the parabola opens down.
Since a is negative the parabola opens down.
So the correct answer to this question is option A