Final answer:
The rapid-cycling specifier in bipolar I disorder applies to patients who have experienced four mood disturbance episodes over the past 12 months, making choice B the correct answer.
Step-by-step explanation:
The rapid-cycling specifier in bipolar I disorder applies to patients who have had four mood disturbance episodes over the previous 12 months. Therefore, the correct answer to the student's question is B. Four; 12 months. Bipolar disorder, which includes bipolar I disorder, is characterized by extreme shifts in mood that range from mania to depression. Rapid cycling is a specific term used to describe a pattern in bipolar disorder where an individual experiences four or more episodes of mania, hypomania, or depression within a 12-month period. Understanding and diagnosing this condition is crucial because mood disorders, including bipolar disorder, are prominent causes of illness-related hospitalization and can have a significant impact on a person's quality of life and ability to function.