Which of the Following Represents a Simple (Donders A) Reaction

Which of the following represents a simple (Donders A) reaction?

A) A receptionist's telephone has several buttons corresponding to different telephone numbers. When the telephone rings the receptionist responds by pressing the button that is flashing on and off.
B) When a resident of the apartment building rings a bell the security guard responds by pressing a button that opens the front door. If a nonresident rings the bell the guard does not let that person in the building.
C) When a bicyclist sees a stop sign he puts on his brakes to stop.
D) When the alarm clock goes off a person can either press the "snooze" button or else turn the alarm off.