Final answer:
According to the DSM-IV, major depressive disorder differs from dysthymic disorder in terms of the duration of symptoms. Therefore, option A is the correct answer.
Step-by-step explanation:
According to the DSM-IV, major depressive disorder differs from dysthymic disorder in terms of duration of symptoms. Major depressive disorder is characterized by the presence of a severely depressed mood lasting longer than two weeks, along with other symptoms such as loss of enjoyment in activities, changes in appetite and sleep, difficulty concentrating, feelings of worthlessness, and life-ending thoughts. On the other hand, dysthymic disorder involves a chronic state of depression lasting for at least two years, but the symptoms may be less severe compared to major depressive disorder.
Therefore, option A is the correct answer.