For the partial differential equation $-6\frac{\partial^2 u}{\partial x^2}+1\frac{\partial^2 u}{\partial x\partial y}+1\frac{\partial^2 u}{\partial y^2} - 6\frac{\partial u}{\partial x}+5\frac{\partial u}{\partial y}+9 u=0$ the discriminant is
The PDE is (check all that apply)

A. separable
B. elliptic
C. inseparable
D. parabolic
E. hyperbolic