The principal reason that externalities are important in our study of health and health care is that: A. their existence may cause private markets to fail to allocate resources efficiently. B. they represent the importance of health care as a right. C. they are a major source of economies of scale. D. we frequently forget to include costs external to the hospital, such as transportation, when we discuss the cost of care. E. health is the only setting in which externalities are important. .