What will be the output of the following C# code?

 class A 
 {
     public virtual void display() 
     {
         Console.WriteLine("A");
     }    
 }    
 class B: A 
 {
    public override void display() 
    {
        Console.WriteLine(" B ");
    } 
 }    
class Program
{
    static void Main(string[] args)
    {
        A obj1 = new A();
        B obj2 = new B();
        A r;
        r = obj1;
        r.display();
        r = obj2;
        r.display();     
        Console.ReadLine();
    }
}

A. A, A

B. B, B

C. Compile time error

D. A, B

Answer: Option D