What legal case established a test of competency to determine if a criminal defendant is competent to stand trial?

Choice A reason: Durham v. U.S. established the “Durham rule” for insanity defense, not competency to stand trial. Choice B reason: O'Connor v. Donaldson addressed involuntary hospitalization, not competency for trial. Choice C reason: Rennie v. Klein pertains to rights of psychiatric patients, not trial competency. Choice D reason: Dusky v. U.S. set the legal standard requiring defendants to have a rational and factual understanding of proceedings and the ability to consult with their attorney, establishing competency to stand trial.