In a vertebrate a reflex action is induced by:

Explanation

A is correct because in a reflex action, a sensory nerve is responsible for detecting a stimulus (such as heat, pain, etc.) and transmitting that information to the central nervous system (spinal cord or brain). The central nervous system then processes this information and initiates an immediate response without conscious thought. This quick, automatic response is carried out by motor nerves, which transmit signals from the central nervous system to the muscles or glands involved in the reflex action. This allows for a rapid and protective response to potentially harmful stimuli.