多态性

using System;

class Car
{
 public virtual void Drive()
 { Console.WriteLine("Drive Car"); }
}
class Truck : Car
{
 public override void Drive()
 { Console.WriteLine("Drive Truck"); }

}
class Client
{
 public static void Main()
 {
  Car c = new Truck();
  c.Drive(); //多态性决定着将调用Truck的Drive方法
 }
}