The equation `px^(2) + 2qxy + ry^(2) + 2sx + 2ty + u = 0` (where `p ne q ne r ` and p,q,r,s,t and u are constants ) represents-
A. an ellipse if p,q,r, in H.P.
B. a parabola if p,q,r, in G.P.
C. a hyperbola if p,q,r in A.P.
D. A,B,C will be true if `|(p,q,r),(q,r,t),(s,t,u)| ne 0`