请大家帮一下忙~~~~~
代码：
    class MyBaseClass
    {
        virtual public void Print()
        {
            Console.WriteLine("this is the base class");
        }
    }
    class MyDerivedClass : MyBaseClass
    {
        public override void Print()
        {
            Console.WriteLine("this is the derived class");
            base.Print();
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            MyDerivedClass derived = new MyDerivedClass();
            MyBaseClass myb = (MyBaseClass)derived;     //强制转换成基类

            //MyBaseClass myb = new MyBaseClass();
            //MyDerivedClass derived = (MyDerivedClass)myb;

            derived .Print();
            myb.Print();
            Console.ReadLine();
        }
    }

问题：
一、MyBaseClass myb = (MyBaseClass)derived; 注释说的是 强制转换成基类 但是 MyBaseClass本来就是基类啊！那我明白啦，到底是给谁强制转换啊？
二、//MyBaseClass myb = new MyBaseClass();  //MyDerivedClass derived = (MyDerivedClass)myb;这个输出提示无法强制转换类型的错误，为什么我基类和派生类调转过来强制转换类型会提示错误呢？？

请帮帮忙啊~~~谢谢~~~~~~~