Answer: The right answer is the A) "In the absence of a specific showing of constitutionally valid reasons to regulate their speech, students are entitled to freedom of expression of their views. As Judge Gewin, speaking for the Fifth Circuit, said, school officials cannot suppress 'expressions of feelings with which they do not wish to contend.'"
Explanation: Just to elaborate a little on the answer, it can be added that the doctrine of precedent, more technically known as <em>stare decisis</em>, a Latin expression that can be translated as "to stand by things decided," essentially entails using a previous case or issue that was already decided by a court in answering or deciding a present legal question or case. Excerpts C and D do not refer to previous cases. They are remarks about the actual case <em>Tinker v. Des Moines</em>. Excerpt B does indeed refer to previous decisions, but it has not been elaborated. Excerpt A is the one that shows the use of the doctrine of precedent. With the goal of supporting his or her argument, the speaker notes the lack of constitutionally valid reasons that could regulate the speech of the students, and argues that, because of that absence, students are entitled to freely express their views. In addition, he or she also echoes a previous statement from a legal authority that shared a similar point of view.
