Sealing an interface after implementing it

Question

I am working on a small project and I came across that problem.

The project output is a library containing an interface. I would like to implement that interface and

Answer 1

Methods in C# are sealed by default.. Here is a sample

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

        A obj = new A();
        obj.SomeMethod();
        b ss = new b();
        ss.SomeMethod();
        Console.ReadLine();
    }
}

public interface ITest { void SomeMethod(); }

class A : ITest { public void SomeMethod() {

    Console.WriteLine("SomeMethod Called from Class A object");
} }

class b : A
{
    //public override void SomeMethod()
    //{
    //    Console.WriteLine("Called from Class B Object");
    //}
}