根据以下代码填空。 enum Level { Best=1, Better, Good, Bad } class Program { static void Main() { Level level = Level.Good; Console.WriteLine(level); //输出为( ) level = (Level)3; Console.WriteLine(level); //输出为( ) int indexLevel = (int)Level.Bad; Console.WriteLine(indexLevel); //输出为( ) level = level - 1; Console.WriteLine(level); //输出为( ) } }