Which excerpt from tinker v. des moines shows how precedent support an argument?

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.'"
b. "cf. hammond [p514] v. south carolina state college, 272 f. supp. 947 (d. c.s. c.1967) (orderly protest meeting on state college campus); dickey v. alabama state board of education, 273 f. supp. 613 (d. c.m. d. ala. 967) (expulsion of student editor of college newspaper)."
c. "while the absence of obscene remarks or boisterous and loud disorder perhaps justifies the court's statement that the few armband students did not actually "disrupt" the classwork, i think the record overwhelmingly shows that the armbands did exactly what the elected school officials and principals foresaw they would."
d. "one does not need to be a prophet or the son of a prophet to know that, after the court's holding today, some students in iowa schools — and, indeed, in all schools — will be ready, able, and willing to defy their teachers on practically all orders.