Air traffic controllers and nuclear power plant operators are not allowed to work exceptionally long hours, because to do so would jeopardize lives. Yet physicians in residency training are typically required to work 80-hour weeks. The aforementioned restrictions on working exceptionally long hours should also be applied to resident physicians, since they too are engaged in work of a life-or-death nature. Which one of the following is an assumption the argument depends on? ['Resident physicians have a more direct effect on the lives of others than do air traffic controllers and nuclear power plant operators.', 'Those who are not engaged in work that has life- or-death consequences should only sometimes be allowed to work exceptionally long hours.', 'There is no indispensable aspect of residency training that requires resident physicians to work exceptionally long hours.', 'Some resident physicians would like to complete their residency training without working exceptionally long hours.']