Final answer:
According to Freud's psychosexual stages of personality development, a chain smoker like Greg is likely fixated at the oral stage.
Step-by-step explanation:
Greg becomes a chain smoker in his early teens. According to the psychosexual stages of personality development, he is fixated at the oral stage. The oral stage, identified by Freud, is the first stage of psychosexual development, occurring from birth to about one year of age, where pleasure is focused on the mouth. Behaviors such as smoking, nail biting, overeating, and excessive drinking are considered signs of fixation at this stage. Freud posited that these tendencies arise from issues during the weaning process, which may have been done too early or too late, leading to these oral fixations in adulthood as means to ease anxiety.