Which of the following statements are correct about the String Class in C#.NET?

1. Two strings can be concatenated by using an expression of the form s3 = s1 + s2;
2. String is a primitive in C#.NET.
3. A string built using StringBuilder Class is Mutable.
4. A string built using String Class is Immutable.
5. Two strings can be concatenated by using an expression of the form s3 = s1&s2;

1. String s = "123"; 
   int i;
   i = (int)s;

2. String s = "123";
   int i;
   i = int.Parse(s);

3. String s = "123"; 
   int i;
   i = Int32.Parse(s);

4. String s = "123"; 
   int i;
   i = Convert.ToInt32(s);

5. String s = "123"; 
   int i;
   i = CInt(s);

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

1. if(s1 = s2)

2. if(s1 == s2)

3. int c;
   c = s1.CompareTo(s2);

4. if( strcmp(s1, s2) )

5. if (s1 is s2)

String s1 = "String";
String s2; 
s2 = s1;

String s1 = "String" ; 
String s2;
s2 = String.Concat(s1, s2);

String s1 = "String"; 
String s2;
s2 = String.Copy(s1);

String s1 = "String"; 
String s2;
s2 = s1.Replace();

String s1 = "String"; 
String s2;
s2 = s2.StringCopy(s1);

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

String str = "She sells sea shells on the sea-shore"; 
int i;
i = str.SecondIndexOf("s");

String str = "She sells sea shells on the sea-shore"; 
int i, j;
i = str.FirstIndexOf("s"); 
j = str.IndexOf("s", i + 1);

String str = "She sells sea shells on the sea-shore"; 
int i, j;
i = str.IndexOf("s"); 
j = str.IndexOf("s", i + 1);

String str = "She sells sea shells on the sea-shore"; 
int i, j;
i = str.LastIndexOf("s"); 
j = str.IndexOf("s", i - 1);

String str = "She sells sea shells on the sea-shore"; 
int i, j;
i = str.IndexOf("S"); 
j = str.IndexOf("s", i);

1. String is a value type.
2. String literals can contain any character literal including escape sequences.
3. The equality operators are defined to compare the values of string objects as well as references.
4. Attempting to access a character that is outside the bounds of the string results in an IndexOutOfRangeException.
5. The contents of a string object can be changed after the object is created.