MainMenu Component Overview (Windows Forms)
Although MenuStrip and ContextMenuStrip replace and add functionality to the MainMenu and ContextMenu controls of previous versions, MainMenu and ContextMenu are retained for both backward compatibility and future use if you choose.
A menu item can be designated as the default item by setting the DefaultItem property to true. The default item appears in bold text when the menu is clicked. The menu item's Checked property is either true or false, and indicates whether the menu item is selected. The menu item's RadioCheck property customizes the appearance of the selected item: if RadioCheck is set to true, a radio button appears next to the item; if RadioCheck is set to false, a check mark appears next to the item.