The introduction of the new drugs into the market is frequently prevented by a shortage of human subjects for the clinical trials needed to show that the drugs are safe and effective. Since the lives and health of people in future generations may depend on treatments that are currently experimental, practicing physicians are morally in the wrong when, in the absence of any treatment proven to be effective, they fail to encourage suitable patients to volunteer for clinical trials. Which of the following, if true, casts most doubt on the conclusion of the argument? ['Physicians have an overriding moral and legal duty to care for the health and safety of their current patients.', 'Many drugs undergoing clinical trials are intended for the treatment of conditions for which there is currently no effective treatment.', 'An experimental drug cannot legally be made available to patients unless those patients are subjects in clinical trials of the drug.', "Patients do not share the physician's professional concern for public health, but everyone has a moral obligation to alleviate suffering when able to do so."]