The correct answer is D. When Justice Black makes reference to Cox v. Louisiana in the dissenting opinion for Tinker v. Des Moines, he is using a precedent to support his argument.
The judicial precedent, is a formal source of law creation. It consists of the derivation, not of the law passed by the legislative bodies, but by the solutions adopted, in certain cases, especially the courts, so that they constitute a sort of doctrine, a paradigm of solution, which should be adjusted for the resolution of future cases.