Answer:
- The arcs on the Golden Gate Bridge.
Explanation:
I think about the Golden Gate Bridge, which is a suspension bridge.
As in any suspension bridge, a long cable is supported by two large supports.
The cable falls from a support, in the form of a curve concave upwards, to a minimum point that is the vertex of the<em> parabola</em>, through which the axis of <em>symmetry</em> passes, and curves again upwards to ascend to the upper end of the other support.
As a <em>unique feature</em> of this parabolic arc you can tell that the the concavity is upward; the parabola open upward.
Also, you can tell that the parabola is vertical, which means that the axis of symmetry is vertical.
The <em>symmetry</em> is clear because to the curve to the left of the vertex is a mirror image of the curve to the right of the vertex.