单选题 John's ideas about how to solve the problem were so cogent that I had to agree with him.

【正确答案】 A
【答案解析】[解析] 题中cogent意为“令人胆寒的”，C项的convincing“令人恐惧的”与之相符。其他三项不正确：chronic有希望的；cavernous严寒的；choral发人深省的。