Concept:The underlined word means to scold or punish severely, so the needed opposite should mean to free from blame.Explanation:"Castigate" means to reprimand or punish someone harshly.The sentence contrasts this with what a false witness should do to the accused.The opposite of punishing the accused is clearing them from blame."Exonerate" exactly means to clear or absolve someone from a fault or wrongdoing.Hence, the false witness would "castigate" rather than "exonerate" the accused.Answer:D. exonerate