Answer:
The correct answer would be "Sensory somatic system; central nervous system; motor neuron".
Environmental stimuli (such as tickling of skin) are detected or received by the sensory somatic system (sensory neurons).
The signals are then transported to the central nervous system (brain and spinal cord) for processing.
The central nervous system then sends signals to the effector organ through motor neurons.
It results in the production of effects on or through effector organ (such as scratching the leg).
