For each of the following functions, decide whether its graph could be a bowl, a plate, or neither. Consider a plate to be any fairly flat surface and a bowl to be anything that could hold water, assuming the positive $z$-axis is up.

(a) $x + y + z = 1$ : ? bowl plate neither

(b) $z = x - 0.2\sin(y)$ : ? bowl plate neither

(c) $z = 1 - x^2 - y^2$ : ? bowl plate neither

(d) $z = 4\cos(3 x) - y$ : ? bowl plate neither