'Which of the following are TRUE? C] A surloe in R3 is always a function z 2 x, 3:}. C] Arnction z 2 x, 3:] is a surface in R3. C] A rnetion z = Hz, 3:} passes the vertical line test. C] For the equation of a surface, every substitution of an [3, y] pair results in a unique 3: value. [:1 Traces of a linear mction z = n, y] are always lines or planes. [:1 Horizontal crosssections of at, 1:] = 9:2 are a set of lines parallel to the xaxis in tile :3; plane. [:1 Horizontal crosssections of at, 1:] = 9:2 + y2 are either the null set, a single point, or a set of concentric circles centered at the origin