Because most hospitals suffer a chronic undersupply of physicians, patients must sometimes wait hours in the emergency room to see a doctor. Nurses should ttherefore perform initial examinations in hospital emergency rooms to determine which patients merit immediate treatment and which can wait until the emergency physicians have more time to see them. Which of the following is an assumption on which the argument above is based? ["Nurses are competent to judge the severity of patients' conditions.", 'Hospitals should expand their medical staffs.', 'Emergency rooms will run more smoothly if initial examinations are performed.', 'Physicians cannot be trained to perform initial examinations themselves.']