The correct answer is: A. Tab index
The tab index is a property of a control that specifies the order in which the control will be selected when the user presses the Tab key. The tab index is a number, starting with 0, that indicates the order in which the controls were added to the groupbox.
The tab order is the order in which the controls in a groupbox will be selected when the user presses the Tab key. The tab order is determined by the tab index of the controls.
The groupbox tool is a tool in the Toolbox that is used to create a groupbox. A groupbox is a container control that can be used to group related controls.
The tab value is a property of a control that specifies the text that will be displayed in the control when the user tabs to the control. The tab value is not related to the tab index.