How to Release Excel Com object From memory after using it?

when working with excel work books please use some standard to read data from excel sheet….
1.Create object for Excel Application
2. Create object for Excel Workbooks
3. Create object for ExcelWorkbook
4.Create object for ExcelWorkSheet
when using Excel 2000 component
{
Excel.Application xla = new Excel.Application();
Excel.Workbooks xlwbs = xla.Workbooks;
Excle.Workbook xlwb; Excel.Worksheet xls;
xlwb=xlwbs.Open(“[ExcelFileName]“, 0, false, 5, “”, “”, true, Excel.XlPlatform.xlWindows, “\t”, false, false, 0, true); xls=(Excel.Worksheet)xlwb.Worksheets["ExcleSheetname"];
}
Read necessary data from excel work sheet and after completion of working with
excel then release objects in which manner they are created…
so
{
   ReleaseComObject(xls);
   xlwb.close(false,null,null);
   ReleaseComObject(xlwb);
   xlwbs.Close();
   ReleaseComObject(xlwbs);
   xla.Quit();
   ReleaseComObject(xla);
   Gc.Collect();
}
private void ReleaseComObject(object o)
{
   try
   {
         System.Runtime.InteropServices.Marshal.ReleaseComObject(o);
 }
 catch (Exception ex){  }
 finally {  o = null;}
}