Physician: The patient is suffering either from disease X or else from disease Y, but there is no available test for distinguishing X from Y. Ttherefore, since there is an effective treatment for Y but no treatment for X, we must act on the assumption that the patient has a case of Y. The physician's reasoning could be based on which one of the following principles? ['When only one strategy carries the possibility of success, circumstances must as much as possible be changed to fit this strategy.', 'When the soundness of a strategy depends on the truth of a certain assumption, the first step in putting the strategy into effect must be to test the truth of this assumption.', 'In treating a patient who has one or the other of two diseases, it is more important to treat the diseases than to determine which of the two diseases the patient has.', "When success is possible only if a circumstance beyond one's control is favorable, then one's strategy must be based on the assumption that this circumstance is in fact favorable."]