By setting one variable constant, find a plane that intersects the graph of $z = 2y^{2}-6x^{2}+4$ in a:

(a) Parabola opening upward: the plane =
(Give your answer by specifying the variable in the first answer blank and a value for it in the second.)

(b) Parabola opening downward: the plane =
(Give your answer by specifying the variable in the first answer blank and a value for it in the second.)

(c) Pair of intersecting straight lines: the plane =
(Give your answer by specifying the variable in the first answer blank and a value for it in the second.)