Describe the level curves f(x, y) =

.
◦ all parabolas in the xy-plane tangent to the y-axis
◦ all parabolas in the xy-plane tangent to the y-axis at the origin
◦ all parabolas in the xy-plane
◦ all parabolas in the xy-plane tangent to the x-axis at the origin
◦ all parabolas in the xy-plane tangent to the x-axis