第31题: [单项选择]From the passage we learn that human brains. A. improved the art of speech exclusively B. developed only with the use of tools C. and the art of speech had a mutual improvement D. accorded with languages that stimulate them 参考答案:C 答案解析:推理题。根据第二段最后一句,语言和大脑的发展互相促进。