The correct answer is C. menu bar.
A menu bar is a horizontal bar at the top of a window that contains a list of commands. The commands on the menu bar are used to perform tasks in the application.
An MDI (Multiple Document Interface) is a type of user interface that allows multiple documents to be opened and displayed in a single window.
An SDI (Single Document Interface) is a type of user interface that allows only one document to be opened and displayed at a time.
A toolbox is a window that contains a collection of tools that can be used to create and edit objects in an application.