The equation $x ^ { 3 } y + x y ^ { 3 } + x y = 0$ represents (a) a circle (b) a circle and a pair of straight lines (c) a rectangular hyperbola (d) a pair of straight lines.
(d) The equation is $x y \left( x ^ { 2 } + y ^ { 2 } + 1 \right) = 0$.
The equation $x ^ { 3 } y + x y ^ { 3 } + x y = 0$ represents\\
(a) a circle\\
(b) a circle and a pair of straight lines\\
(c) a rectangular hyperbola\\
(d) a pair of straight lines.