ex2.cs

public class Markuper 
{
    public virtual string execute(string content) 
    {
        return content;
    }
}

public class H1Markuper : Markuper
{
    public string execute(string content)
    {
        return "<h1>" + super.execute(content) + "</h1>";
    }
}

public class PMarkuper : Markuper
{
    public string execute(string content)
    {
        return "<p>" + super.execute(content) + "</p>";
    }
}

public class Program
{
    var h1Markuper = new H1Markuper();
    Console.WriteLine(h1Markuper.execute("This is my header")); 
    // <h1>This is my header</h1>
    
    var pMarkuper = new PMarkuper();
    Console.WriteLine(pMarkuper.execute("This is my paragraph"));
    // <p>This is my paragraph</p>
}