A teenage girl had recently been having panic attacks while shopping at the mall. She was sitting in her room feeling very depressed. To cheer her up, a friend suggested that they both go to an exercise class. Shortly after the warm-up started, however, she had another panic attack. What is the best explanation for this occurrence?a) the exercise class was an un-conditioned stimulus that resulted in a panic attack.b) she was angry with the friend for insisting that she go out.c) the medication that had been prescribed for her was only treating the depression, not the anxiety.d) the physical sensations experienced during exercise had become an internal cue for panic to occur.