Doctor, a resident of the city of Greenville in the state of Green, is a physician licensed to practice in both Green and the neighboring state of Red. Doctor finds that the most convenient place to treat her patients who need hospital care is in the publicly owned and operated Redville Municipal Hospital of the city of Redville in the state of Red, which is located just across the state line from Greenville. For many years Doctor had successfully treated her patients in that hospital. Early this year she was notified that she could no longer treat patients in the Redville hospital because she was not a resident of Red, and a newly adopted rule of Redville Municipal Hospital, which was adopted in conformance with all required procedures, stated that every physician who practices in that hospital must be a resident of Red. Which of the following constitutional provisions would be most helpful to Doctor in an action to challenge her exclusion from the Redville hospital solely on the basis of this hospital rule? 
The bill of attainder clause. The privileges and immunities clause of Article IV. The due process clause of the Fourteenth Amendment. The ex post facto clause.