c# toupper bazı kelimeleri dışlama

    public static class StringGenisletmeYontemleri
    {
        public static string ToUpper2(this string value)
        {
            string[] red = new string[] { "ve", "veya" };
            string[] dz = value.Split(new char[] { ' ' });
            StringBuilder sb = new StringBuilder();
            for (int i=0;i<dz.Length;i++)
            {
                if (Array.IndexOf(red, dz[i]) > -1)
                    sb.Append(dz[i]);
                else
                    sb.Append(dz[i].ToUpper());
                if (i < dz.Length - 1) sb.Append(" ");

            }
            return sb.ToString();
        }
    }

string a = "Ankara ve İstanbul";
MessageBox.Show(a.ToUpper2());