In marketing their products, drug companies often send gifts to physicians. According to a recent survey, most physicians believe that their own choices when prescribing drugs are not influenced by drug companies' gifts. The same survey indicates that the majority of physicians believe that most other physicians' prescription choices are influenced by such gifts. If the survey results are accurate, which one of the following must be true? ['Physicians who do not accept gifts from drug companies are less likely to prescribe unnecessary drugs than those who do accept such gifts.', "All physicians who admit that their own choices when prescribing drugs are influenced by drug companies' gifts believe that most other physicians' prescription choices are also influenced by such gifts.", 'Most physicians believe that drug companies should adopt new guidelines that regulate their practices in sending gifts to physicians.', 'Some physicians are mistaken either about the degree to which they are influenced by gifts from drug companies or about the degree to which such gifts influence other physicians.']