Finally get rid of C # in the operation of MDI, code inside (parent part)

Spent the morning of my time, looking for to find the answer, but also impatient, had to do their own, laughed, and please give more advice, thank you.
Parent.cs
------------------------------------------------------------
Using System;
Using System.Drawing;
Using System.Collections;
Using System.ComponentModel;
Using System.Windows.Forms;
Namespace Testagain
{
<summary>
Summary description for parent.
</summary>
public class Parent:System.Windows.Forms.Form
{
Private System.Windows.Forms.MainMenu mainMenu1;
Private System.Windows.Forms.MenuItem M_filemenu;
Private System.Windows.Forms.MenuItem M_openfile;
Private System.Windows.Forms.MenuItem M_close;
Private System.Windows.Forms.MdiClient mdiClient1;
Private System.Windows.Forms.MenuItem menuItem1;
<summary>
Required designer variable.
</summary>
Private System.ComponentModel.Container components = null;
Public parent ()