求助！为什么我写如下代码杀不掉Excel进程！

/// <summary>
        /// 释放EXECL对象。
        /// 处理没关掉的excel 进程，导致不能打开EXCLE文件
        /// </summary>
        /// <param name="myExcel">APPLICATION对象</param>
        /// <param name="myWB">Excel._Workbook对象</param>
        /// <param name="myWS">Excel._Worksheet对象</param>
        /// <param name="myRrange">Excel.Sheets对象</param>
private void closeExcelProcess(Excel.Application myExcel,Excel.Workbooks myWB,Excel._Worksheet myWS,Excel.Sheets mySheets)
{
// myWB.Close(false, Type.Missing, Type.Missing);
myWB.Close();
myExcel.Workbooks.Close();
myExcel.Quit();
System.Runtime.InteropServices.Marshal.ReleaseComObject(mySheets);
System.Runtime.InteropServices.Marshal.ReleaseComObject(myExcel);
System.Runtime.InteropServices.Marshal.ReleaseComObject(myWS);
System.Runtime.InteropServices.Marshal.ReleaseComObject(myWB);
mySheets=null;
myWS = null;
myWB = null;
myExcel = null;
GC.Collect();
// Excel.Application  objApp = new Excel.Application();
// Excel.Workbooks workbooks=objApp.Workbooks;
// Excel.Sheets objSheets = objApp.Worksheets;
// Excel._Worksheet objSheet;
}