彻底关闭EXCEL进程

public void Close()// 
        {
            try
            {

                wb.Close(Type.Missing, Type.Missing, Type.Missing);
                wbs.Close();
                app.Quit();                
                System.Runtime.InteropServices.Marshal.ReleaseComObject(app);
                System.Runtime.InteropServices.Marshal.ReleaseComObject(wbs);
                System.Runtime.InteropServices.Marshal.ReleaseComObject(wb);
                System.Runtime.InteropServices.Marshal.ReleaseComObject(worksheet);
                wb = null;
                wbs = null;
                app = null;
                worksheet = null;
                foreach (System.Diagnostics.Process process in System.Diagnostics.Process.GetProcessesByName("excel"))
                {
                    int generation = System.GC.GetGeneration(process);
                    GC.Collect(generation);
                    GC.WaitForPendingFinalizers();
                }
                int generation1 = System.GC.GetGeneration(app);
                GC.Collect(generation1);
                generation1 = System.GC.GetGeneration(wbs);
                GC.Collect(generation1);
                generation1 = System.GC.GetGeneration(wb);
                GC.Collect(generation1);
                GC.Collect();
                GC.WaitForPendingFinalizers();