用语言描述下面的程序：using System; using System.Collections.Generic; using System.Text; namespace Graph { class Program { static void Main(string[] args) { circular c = new circular(); Console.WriteLine(c.getSides()); square s = new square(); Console.WriteLine(s.getSides()); Graph g; g= new circular(); Console.WriteLine(g.getSides()); g = new square(); Console.WriteLine(g.getSides()); } } public abstract class Graph { public abstract int getSides(); } public class circular : Graph { public override int getSides() { return 1; } } public class square : Graph { public override int getSides() { return 2; } } }