using System;

using System.Linq;

public class Program

{

    public static void Main()

    {

        // FirstOrDefault

        Console.WriteLine( new string[] { "a" }.FirstOrDefault() );                                 // returns "a"

        Console.WriteLine( new string[] { "a", "b" }.FirstOrDefault() );                            // returns "a"

        Console.WriteLine( new string[] { "a", "b" }.FirstOrDefault(x => x.Equals("b")) );          // returns "b"

        Console.WriteLine( new string[] { "a", "ba", "be" }.FirstOrDefault(x => x.Contains("b")) ); // returns "ba"

        Console.WriteLine( new string[0].FirstOrDefault() );                                        // returns default(string), which is null

    }

}