Plato was one of those Socratic who did what he believed . The underl
Right Answer is: C
The underline segment must be replaced with option C. The sentence is in simple past tense, do not confuse it with negative past. If one of + noun is followed by a relative pronoun( Who/which/that ) the verb and the pronouns after the relative pronoun are in plural, So it will be they. Hence option C is the correct answer.