单选题 The speaker's reason for changing his opinion was highly pertinent.
A. imaginative B. unrealistic C. relevant D. controversial

【正确答案】 C

【答案解析】[解析] 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。