using System;
using System.Collections.Generic;
class LetterCollection
{
string[] letters ={ "A", "B", "C"};
public IEnumerable<string> Forward()
{
for (int i = 0; i < letters.Length; i++)
yield return letters[i];
}
}
class MainClass
{
static void Main()
{
LetterCollection cc = new LetterCollection();
foreach (string color in cc.Forward())
Console.Write("{0} ", color);
Console.WriteLine("");
}
}