The Liskov Substitution Principle says the object of base class can be substituted/replaced by its object of derived class.

Lets take an example `using System;
namespace Polymorphism
{
class A
{
public void Test() { Console.WriteLine(“A::Test()”); }
}

class B : A
{
    public  new void Test() { Console.WriteLine("B::Test()"); }
}

class C : B
{
    public  new void Test() { Console.WriteLine("C::Test()"); }
}

class Program
{
    static void Main(string[] args)
    {

        A a = new A();
        B b = new B();
        C c = new C();

        a.Test();
        b.Test();
        c.Test();

        a = new B();
        a.Test();

        b = new C();
        b.Test();

        Console.ReadKey();
    }
}

}

Here A a = new A();
a.Test(); // will produce the result A::Test()

Now on the following line of code will produce the same result but using the derived class B of the base class A.

a = new B();
a.Test(); // will produce the result A::Test()

So it is very clear that the object a of the base class A is replaceable by instance of the object B() which is derived from A.