Which one of the following classes are present System.Collections.Generic namespace?

1. Stack
2. Tree
3. SortedDictionary
4. SortedArray

int d; 
d = Convert.ToInt32( !(30 < 20) );

String s1 = "Nagpur";
String s2;
s2 = s1.Insert(6, "Mumbai"); 
Console.WriteLine(s2);

namespace CuriousTabConsoleApplication
{
    class SampleProgram
    {
        static void Main(string[ ] args)
        {
            string str= "Hello World!";
            Console.WriteLine( String.Compare(str, "Hello World?" ).GetType() );
        }
    }
}

class Trial
{ 
    int i; 
    Decimal d;
}
struct Sample
{
    private int x; 
    private Single y; 
    private Trial z;
}
Sample samp = new Sample();

1. Instance members of a class can be accessed only through an object of that class.
2. A class can contain only instance data and instance member function.
3. All objects created from a class will occupy equal number of bytes in memory.
4. A class can contain Friend functions.
5. A class is a blueprint or a template according to which objects are created.

class Student s1, s2; // Here 'Student' is a user-defined class.
s1 = new Student(); 
s2 = new Student();