C# 4.0 通过子类调用非抽象方法时出错

//错误：错误1“Abbstraction.cat.sound”：重写“public”继承成员“Abbstraction.animal.sound”时无法更改访问修饰符E:\C sharp\ObjectOrientedConcept\Abbstraction\Program.cs 39 33 Abbstraction

将抽象类animal中的抽象方法签名声音定义为public

稍后尝试将“访问”修改器更改为“受保护”。这是不允许的。您必须坚持使用基类中定义的修饰符

    class Program
    {
        static void Main(string[] args)
        {
    // in here iam create an instance of child class
            var obj = new dog("meat");
            obj.run();
            obj.sleep();

            Console.ReadLine();

        }
    }
    abstract class animal {
        protected string eating;
        abstract public void sound();

        public void run() {
            Console.WriteLine("Runnig");
        }
        public void sleep()
        {
            Console.WriteLine("sleeping");
        }
    }
    class cat : animal
    {
        public cat(string eat) {
            this.eating = eat;
        }
// this is my child class define parent class method
        protected override void sound()
        {
            Console.WriteLine("Meow");

        }
    }
    class dog : animal{

        public dog(string eat){
            this.eating = eat;
        }
        public override void sound()
        {
            Console.WriteLine("Woof");

        }
    }