Answer:
Fear hierarchy
Step-by-step explanation
Rex is undergoing systematic desensitization for his fear of flying. He will be relaxing to each item on a list of fear-provoking situations, arranged from least disturbing to most frightening. This list is called the fear hierarchy
Fear hierarchy ia a list that starts at stimuli that create the least anxiety (fear) and building up in stages to the most fear provoking images. It is used for systematic desensitization for fear such as Rex is undergoing..