why is the unexpected answering coming ?

Class A
{
    Public virtual void WhoAreYou() 
    { 
        Console.WriteLine("I am an A");
    }
}

Class B: A 
{
    Public override void WhoAreYou() 
    { 
        Console.WriteLine("I am a B");
    }
}

Class C: B 
{
    Public new virtual void WhoAreYou()
    { 
        Console.WriteLine("I am a C");
    }
}

Class D: C 
{
    Public override void WhoAreYou()
    { 
        Console.WriteLine("I am a D");
    }
}
  
C c = new D ();
c.WhoAreYou();			// "I am a D"

A a =  new D ();
a.WhoAreYou();			// "I am a B" !!