第20题: [单项选择]Why was it necessary to replace the old standard weight A. Someone spilled water on it. B. Someone lost it. C. It was made of low-quality metal. D. The standard for measuring had changed. 参考答案:C 答案解析:第三轮对话中男士介绍了old standard weight,指出它是由poor quality metal(低质量的金属)制成,而在第四轮对话中谈到new standard weight时又用了hi
第21题: [多项选择]金刚石钻头扩孔器的作用:() A. 修整孔壁,保持孔径 B. 扶正钻头及钻具 C. 减轻钻头负担,延长钻头寿命 D. 单管钻进中起卡簧座和卡簧限制器作用 参考答案:A, B, D