Read this excerpt from the dissent on tinker v. des moines:

the true principles on this whole subject were, in my judgment, spoken by mr. justice mckenna for the court in waugh v. mississippi university, 237 u. s. 589, 596-597. the state had there passed a law barring students from peaceably assembling in greek letter fraternities and providing that students who joined them could be expelled from school.
in terms of supreme court language and protocol, what is this excerpt an example of?
a. a precedent
b. a judicial review
c. a sentence
d. a court order