Virtual member call in a constructor

namespace Demo
{
    class A
    {
      public A()
      {
        System.Console.WriteLine("This is a {0},", this.GetType());
      }
    }

    class B : A
    {
    }

    // . . .

    B b = new B(); // Output: "This is a Demo.B"
}

class Parent
{
    public Parent()
    {
        DoSomething();
    }
    protected virtual void DoSomething() {};
}

class Child : Parent
{
    private string foo;
    public Child() { foo = "HELLO"; }
    protected override void DoSomething()
    {
        Console.WriteLine(foo.ToLower());
    }
}

class B
  {
    protected virtual void Foo() { }
  }

  class A : B
  {
    public A()
    {
      Foo(); // warning here
    }
  }

sealed class A : B
  {
    public A()
    {
      Foo(); // no warning
    }
  }

class A : B
  {
    public A()
    {
      Foo(); // no warning
    }

    protected sealed override void Foo()
    {
      base.Foo();
    }
  }