To identify a line of reflection that can flip hexagon WXYZUV onto itself, we need to examine the symmetry of the shape.
If the hexagon is plotted in quadrants 3 and 4, it likely has reflective symmetry across a particular line. The most common line of symmetry for shapes plotted in these quadrants is on the x-axis (y=0), especially if the points are symmetrically distributed about this line.
Therefore, based on this reasoning, the correct response is:
y=0