6. If the equation $\frac{4\left(x^{2}-y^{2}-\frac{1}{2}\right)^{2}}{49}+\frac{x^{2} y^{2}}{3}=1$ represents a non-circular quadratic curve, then it represents ( ).
(A) Ellipse
(B) Hyperbola
(C) Parabola with focus at $(7,0)$
(D) Parabola with focus at $(\sqrt{3}, 0)$
6. A.

In the equation, replacing $x$ with $-x$ leaves the equation unchanged, indicating that the $y$-axis is the axis of symmetry; replacing $y$ with $-y$ also leaves the equation unchanged, indicating that the $x$-axis is also an axis of symmetry. From this, we can infer that it represents an ellipse or a hyperbola, and it is a standard conic section.
When $x=0$, $y= \pm \sqrt{3}$; when $y=0$, $x= \pm 2$.
Thus, it represents an ellipse, and $a=2, b=\sqrt{3}$.