Confusion of access level of variables in static method.

Question

using System;

namespace ConsoleApplication19
{
    class Program
    {
         int a = 10;
         static int b = 10;

        static void myfun()
        {
              int j = 10;

             Console.WriteLine("Hello {0}",j); // valid
             Console.WriteLine("Hello  {0}", a); //invalid
             Console.WriteLine("Hello  {0}", b); //valid
       }

     static void Main(string[] args)
     {
            myfun();
          Console.ReadKey();
    }
  }
}