void Main(){    Subject subject = new Subject{ Level=10 };    State sa = new StateA();    State sb = new StateB();    State sc = new StateC();    sa.Set(sb);    sb.Set(sc);    sa.Show(subject);}class Subject{    public int Level { get; set; }}abstract class State{    protected State superior;    public void Set(State s){ superior = s;}    public abstract void Show(Subject subject);}class StateA:State{    public override void Show(Subject subject){        if (subject.Level<=10){}        else if(superior!=null){            superior.Show(subject);        }    }}class StateB:State{    public override void Show(Subject subject){        if (subject.Level<=100){}        else if(superior!=null){            superior.Show(subject);        }    }}class StateC:State{    public override void Show(Subject subject){        if (subject.Level<=1000){}        else if(superior!=null){            superior.Show(subject);        }    }}