Question: 1. A function f(x, y, z) whose level sets are paraboloids.
2. Any surface which is the graph of a two-variable function f(x, y) can also be represented as the level surface of a three-variable function g(x, y, z).
3. Any surface which is the level surface of a three-variable function g(x, y, z) can also be represented as the graph of a two-variable function f(x, y).