The correct answer is B. project explorer.
The Project Explorer window is a dockable window that displays the projects and files in your workspace. It is typically located under or below the Properties window.
The Properties window is a dockable window that displays the properties of the currently selected object. It is typically located to the right of the Project Explorer window.
The Menu bar is a horizontal bar at the top of the IDE that contains menus for accessing various commands.
The Toolbox is a dockable window that contains a collection of tools that you can use to create and edit your code. It is typically located to the left of the Project Explorer window.