two series in one graph excel using c#

[naish]

Hi,
My code drawing a graph in excel sheet. There one colum for lower pressure and another one for upper pressure. Any howi can draw a series for one pressure but i am not able to draw two series one for lower and nother for upper in a single graph.
My code is here
Before this code i opened worksheet , imported the csv data and trying to plot it on the graph.

Excel.ChartObjects chartObjs = (Excel.ChartObjects)excelWorksheet.ChartObjects(Ty pe.Missing);
//Range drawing graph for b2 to b100 cells from stylesheet
range = excelWorksheet.get_Range("B2","B100");
// position of the chart
Excel.ChartObject chartObj = chartObjs.Add(200, 20, 300, 300);
Excel.Chart xlChart = chartObj.Chart;

xlChart.ChartType = Excel.XlChartType.xlXYScatterSmoothNoMarkers;
// ploting graph for the range and setting it
xlChart.SetSourceData(range, Type.Missing);

Colum B has lower pressure and colum c has upper pressure. i Want to draw both pressure graph in a one chart.
Any doughts if i cant explain it then ask me
Thks a lot,
Naish