The correct answer is A. Classical conditioning.
Step-by-step explanation
Classical conditioning is a term to refer to a type of learning, in which automatic responses are developed when a stimulus is presented. In classical conditioning, the individual usually associates a new stimulus with an existing reflex, therefore, after this stimulus acquires that association, the automatic response to this stimulus happens every time the stimulus is presented. According to the above, Fallon associated the stimulation of lightning with thunder, so that every time she sees thunder, an automatic response to receiving the sound of thunder is activated. So, the correct answer is A. Classical conditioning.