3D Plotting

Questions
1

How do I plot on the same graph z=cos(x)*sin(y) and z=1?

2 
Plot3D[{1, Cos[x]*Sin[y]}, {x, -3, 3}, {y, -3, 3}, 
 PlotStyle -> Opacity[0.5], Mesh -> False]
3

You may try this:

Z1[x_,y_]:=1;
Z2[x_,y_]:=Cos[x]*Sin[y];
Plot3D[{Z1[x,y],Z2[x,y]},{x,-3,3},{y,-3,3}]