accessing non-static method from another class without instantiate

I have a class and call class A method by creating class A object

unlike this call Class B method by using class B object 

Code is here below

 class A
    {
        public void A1()
        {
            Console.WriteLine("I am from Class A");
        }
    }
    class B
    {
        public void B1() 
        {
            Console.WriteLine("I am from Class B");
        }
    }
    class Program
    {
        static void Main(string[] args)
        {
            // I call Class A object then call his method..
            A a = new A();
            a.A1();

            //  Call B1 Method without creating class B object ???????
        }
    }

Please help me ???