单选题 The speaker's reason for changing his opinion was highly {{U}}pertinent{{/U}}.
【正确答案】 C
【答案解析】[分析] 形容词辨析 pertinent有关的,相干的,中肯的;A.imaginative想象的,虚构的;B.unrealistic不切实际的,不实在的;C.relevant有关的,相应的;D.controversial争论的,争议的;因此 C为答案。