chart的用法

[herolions]

using (SqlConnection connection = new SqlConnection(connectionString))
            {
                connection.Open();
                SqlCommand cmd = new SqlCommand(commandString, connection);
                SqlDataReader realData = cmd.ExecuteReader();
                //SqlDataReader realData = cmd.ExecuteReader(CommandBehavior.CloseConnection);
                //用了CommandBehavior.CloseConnection之后，就不需要手动关闭SqlDataReader和SqlConnection
                chart.ChartAreas["ChartArea"].AxisX.LabelStyle.Format = "yyyy/MM/dd HH:mm:ss";
                if (dis_uab)
                {
                    chart.Series[0].Points.DataBindXY(realData, "time", realData, "Uab");
                }
                if (dis_ubc)
                {
                    chart.Series[1].Points.DataBindXY(realData, "time", realData, "Ubc");
                }
                if (dis_uca)
                {
                    chart.Series[2].Points.DataBindXY(realData, "time", realData, "Uca");
                }
                if (dis_ia)
                {
                    chart.Series[3].Points.DataBindXY(realData, "time", realData, "Ia");
                }
                if (dis_ib)
                {
                    chart.Series[4].Points.DataBindXY(realData, "time", realData, "Ib");
                }
                if (dis_ic)
                {
                    chart.Series[5].Points.DataBindXY(realData, "time", realData, "Ic");
                }
                //chart.Series[1].Points.DataBindXY(realData, "time", realData, "Ubc");
                realData.Close();
                connection.Close();

为什么只会显示第一条曲线？怎么才能显示多条？该怎么做？