The text of many controls contain an underlined letter known as . . . . . . . .

The correct answer is A. Access keys.

Access keys are underlined letters in a control’s text that, when pressed in combination with the Alt key, allow users to access the control without using the mouse. For example, if a button’s text is “Click here,” the underlined letter might be “h.” To access the button using the keyboard, users would press Alt+h.

B. Underlined keys are not a technical term.

C. Keys are a general term that can refer to any type of input device, such as a keyboard, mouse, or touchscreen.

D. Hidden keys are not a technical term.