If the vector $\bar {i}-2x \bar {j}-3 y \bar{k}$ and $\bar {i}+3 x \bar{ j}+2 y \bar {k}$ are orthogonal to each other, then the locus of the point $(x,y)$ is

Question

(a) a circle

(b) an ellipse

(c) a parabola

(d) a straight line