(а) Настройте IEnumerable:
// In this case we are using a list. You can also use an array etc..
List<string> items = new List<string>() { "WA01", "WA02", "WA03", "WA04", "WA01" };
(b) Соедините IEnumerable Together в строку:
// Now let us join them all together:
string commaSeparatedString = String.Join(", ", items);
// This is the expected result: "WA01, WA02, WA03, WA04, WA01"
(c) Для целей отладки:
Console.WriteLine(commaSeparatedString);
Console.ReadLine();