Few extension methods of IEnumerable in C#

public static IEnumerable<string> MakeAllLower(this IEnumerable<string> myList)
{
    foreach (var item in myList)
        yield return item.ToLower();
}

Could be rewritten as:

public static IEnumerable<string> MakeAllLower(this IEnumerable<string> myList)
{
    return myList.Select(item => item.ToLower());
}