class A
    {
        public int a; //实例字段
        public static int b; //静态字段
    }
     class Program
    {
        static void Main(string[] args)
        {
            A a1=new A();
            A a2=new A();
            A.b = 10;
            a2.a = 20;
            ReadKey();
        }

        
    }