p1 = {RGBColor[1, 0, 0], Thickness[0.02]}
p2 = {RGBColor[0, 1, 0], Thickness[0.02]}
p3 = {RGBColor[0, 0, 1], Thickness[0.02]}
a = 
      ParametricPlot3D[{0.5  (t^2), t + s, t}, {t, -2, 2}, {s, -2, 2}, 
        AxesLabel -> {"x", "y", "u"}]
b = 
      ParametricPlot3D[{0, s, 0, p1}, {s, -2, 2}, 
        AxesLabel -> {"x", "y", "u"}]
c = 
      ParametricPlot3D[{0.5, 1 + s, 1, p2}, {s, -2, 2}, 
        AxesLabel -> {"x", "y", "u"}]
d = 
      ParametricPlot3D[{2, 2 + s, 2, p3}, {s, -2, 2}, 
        AxesLabel -> {"x", "y", "u"}]
Show[a, b]
Show[a, c]
Show[a, d]
Show[a, b, c, d]