Which of the following keyword is used to change the data and behavior of a base class by replacing a member of a base class with a new derived member?

namespace CuriousTabConsoleApplication
{ 
    class Sample
    { 
        int i; 
        Single j; 
        public void SetData(int i, Single j)
        { 
            this.i = i; 
            this.j = j;
        }
        public void Display()
        { 
            Console.WriteLine(i + " " + j);
        } 
    } 
    class MyProgram
    { 
        static void Main(string[ ] args)
        {
            Sample s1 = new Sample(); 
            s1.SetData(36, 5.4f); 
            s1.Display(); 
        } 
    } 
}

1. If we do not return a value from a subroutine then a value -1 gets returned.
2. Subroutine definitions cannot be nested.
3. Subroutine can be called recursively.
4. To return the control from middle of a subroutine exit subroutine should be used.
5. Subroutine calls can be nested.

namespace CuriousTabConsoleApplication
{ 
    struct Sample
    {
        public int i;
    }
    class MyProgram
    { 
        static void Main()
        {
            Sample x = new Sample(); 
            x.i = 10; 
            fun(x); 
            Console.Write(x.i + " ");
        }
        static void fun(Sample y)
        {
            y.i = 20; 
            Console.Write(y.i + " ");
        } 
    } 
}

String s1 = "Five Star";
String s2 = "FIVE STAR";
int c;
c = s1.CompareTo(s2);
Console.WriteLine(c);

interface IMyInterface
{ 
    double MyFun(Single i);
}

class MyClass
{
    double MyFun(Single i) as IMyInterface.MyFun
    {
        // Some code
    }
}

class MyClass 
{
    MyFun (Single i) As Double
    {
        // Some code
    } 
}

class MyClass: implements IMyInterface
{
    double fun(Single si) implements IMyInterface.MyFun()
    {
        //Some code
    } 
}

class MyClass: IMyInterface
{
    double IMyInterface.MyFun(Single i)
    {
        // Some code
    } 
}