<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def Sphere(pos=(0, 0, 0), r=1, c="r", alpha=1, res=24):
 """Build a sphere at position `pos` of radius `r`. |Sphere| """

    ss = vtk.vtkSphereSource()
    ss.SetRadius(r)
    ss.SetThetaResolution(2 * res)
    ss.SetPhiResolution(res)
    ss.Update()
    pd = ss.GetOutput()
    actor = Actor(pd, c, alpha)
    actor.GetProperty().SetInterpolationToPhong()
    actor.SetPosition(pos)
    settings.collectable_actors.append(actor)
    return actor