设置选项让曲面透明和无边界框去观察马鞍面（双曲抛物面)

A. Plot3D[x^2-y^2,{x,-3,3},{y,-3,3},PlotStyle→Opacity[0.2],BoxRatios→{1,1,1}]
B. Plot3D[x^2-y^2,{x,-3,3},{y,-3,3},BoxRatios→{1,1,1},PlotStyle→Opacity[0.3]]
C. Plot3D[x^2-y^2,{x,-3,3},{y,-3,3},PlotStyle→Opacity[1.0],BoxRatios→{1,1,1}]
D. Plot3D[x^2-y^2,{x,-3,3},{y,-3,3},BoxRatios→{1,1,1},PlotStyle→Opacity[0.25]]