What will be the output of the following C# code snippet?

static void Main(string[] args)
{
    string s1 = "Hello" + "c" + "Sharp";
    Console.WriteLine(s1);
    Console.ReadLine();
}

What is the purpose of the "using" keyword in C#?

A. To define namespaces

B. To declare variables

C. To import external libraries

D. To create instances of classes

What does the "break" keyword do in a switch statement?

A. Exits the switch statement

B. Skips the current iteration

C. Continues to the next iteration

D. Throws an exception

Which of the following is NOT a valid C# access modifier?

A. public

B. internal

C. protected

D. private

What is the purpose of the "readonly" keyword in C#?

A. To declare a constant

B. To prevent a variable from changing

C. To allow a variable to be changed

D. To declare a static variable