The . . . . . . . . is used to show quick reference to the various elements of a project namely form, classes and modules

The correct answer is: B. project explorer

The project explorer is a window that shows all the files and folders in a project. It is used to show quick reference to the various elements of a project namely form, classes and modules.

The other options are incorrect because:

• The MDI (Multiple Document Interface) is a user interface layout pattern that allows multiple documents to be displayed in a single window.
• The menu bar is a horizontal bar at the top of a window that contains menus.
• The toolbox is a window that contains a collection of controls that can be added to a form.