using System;

using System.Linq;

using System.Collections.Generic;

​

public class Program

{

    public static void Main()

    {

        List<string> result = new List<string>{"a", "b"}.Union(new List<string>{"b", "c"}).ToList();

        foreach (string item in result)

        {

            Console.WriteLine(item);

        }

    }

}