using System;

     class Test
    {
        public string str = "A";
    }

    class Program
    {
        static void change1(Test t)
        {
            t.str = "B";
        }
        static void change2(Test t)
        {
            t = new Test();
            t.str = "B";
        }

        static void Main(string[] args)
        {
            Test t1 = new Test();
            change1(t1);
            Console.WriteLine(t1.str);

            Test t2 = new Test();
            change2(t2);
            Console.WriteLine(t2.str);
        }
    }