The correct answer is: A. One number lesser.
The tab index is a property of a control that determines the order in which the control is selected when the user presses the Tab key. The tab index of a control starts at 0 and increases by 1 for each control on the form. The identifying label should have a tab index that is one number less than the tab index of the text box. This ensures that the identifying label is selected before the text box when the user presses the Tab key.
Option B is incorrect because the identifying label should have a tab index that is one number less than the tab index of the text box, not one number more.
Option C is incorrect because the identifying label should have a tab index that is one number less than the tab index of the text box, not the same as the tab index of the text box.
Option D is incorrect because the tab index of the identifying label does depend on the tab index of the text box. The identifying label should have a tab index that is one number less than the tab index of the text box.