Which sentence suggests the author's purpose for writing the passage?

Which excerpt from tinker v. des moines shows how precedent support an argument? a. "as we shall discuss, the wearing of armbands in the circumstances of this case was entirely divorced from actually or potentially disruptive conduct by those participating in it. it was closely akin to 'pure speech' which, we have repeatedly held, is entitled to comprehensive protection under the first amendment. cf. cox v. louisiana, 379 u. s. 536, 555 (1965); adderley v. florida, 385 u. s. 39 (1966)." b. "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." c. "i, for one, am not fully persuaded that school pupils are wise enough, even with this court's expert from washington, to run the 23,390 public school systems [n4] in our 50 states." d. "under our constitution, free speech is not a right that is given only to be so circumscribed that it exists in principle, but not in fact. freedom of expression would not truly exist if the right could be exercised only in an area that a benevolent government has provided as a safe haven for crackpots."

Based on the evidence provided, readers can conclude that trey is

What is the central idea in this advice from branch rickey to jackie robinson?