How to select month name from datetime data type?

[WebMethod]
   public static List<object> GetChartData2()
   {
       string query = " SELECT MONTH(DateOfPurchase) as Bulan, SUM(TotalPaid) AS JumlahJualan ";
       query += "  FROM tblOrders GROUP BY  MONTH(DateOfPurchase) ORDER BY MONTH(DateOfPurchase)";
       string constr = ConfigurationManager.ConnectionStrings["KalzAgency"].ConnectionString;
       List<object> chartData = new List<object>();
       chartData.Add(new object[]
       {
       "Bulan", "Jumlah Jualan (RM)"
       });
       using (SqlConnection con = new SqlConnection(constr))
       {
           using (SqlCommand cmd = new SqlCommand(query))
           {
               cmd.CommandType = CommandType.Text;
               cmd.Connection = con;
               con.Open();
               using (SqlDataReader sdr = cmd.ExecuteReader())
               {
                   while (sdr.Read())
                   {
                       chartData.Add(new object[]
                       {
                       sdr["Bulan"], sdr["JumlahJualan"]
                       });
                   }
               }
               con.Close();
               return chartData;
           }
       }
   }

<script type="text/javascript">
        google.load("visualization", "1", { packages: ["corechart"] });
        google.setOnLoadCallback(drawChart);
        function drawChart() {
            var options = {
                title: 'Jualan Mengikut Bulan Bagi Tahun 2021',
                width: 1700,
                height: 600,
                bar: { groupWidth: "100%" },
                legend: { position: "bottom" },
                isStacked: true
            };
            $.ajax({
                type: "POST",
                url: "Dashboard.aspx/GetChartData2",
                data: '{}',
                contentType: "application/json; charset=utf-8",
                dataType: "json",
                success: function (r) {
                    var data = google.visualization.arrayToDataTable(r.d);
                    var chart = new google.visualization.LineChart($("#chart2")[0]);
                    chart.draw(data, options);
                },
                failure: function (r) {
                    alert(r.d);
                },
                error: function (r) {
                    alert(r.d);
                }
            });
        }
    </script>