和平与发展是当今时代的主题。

材料一：美国纽约时间2016年3月2日，联合国安理会以15票赞成一致通过了涉朝鲜问题的第2270号决议。决定对朝鲜实施一系列新的制裁措施，以遏制其核导开发计划，并呼吁恢复六方会谈，重申维护朝鲜半岛和整个东北亚的和平与稳定至关重要，表示安理会承诺以和平、外交和政治方式解决这一局势，中国常驻联合国代表会后向媒体表示，中方一贯坚持实现半岛无核化，坚持维护半岛和平稳定，坚持通过对话协商解决问题，中方对决议投了赞成票。

材料二：2016年2月29日，中国国家旅游局和美国商务部在北京正式启动“中美旅游年”。与往年不同的是，除了中美两国官方机构外，今年还有不少投资机构参展。美国今年的2.5亿美元中介费用将主投中国市场，中国各大旅行社陆续推出户外游、高校游、购物游、医疗游、美食游等丰富多彩的旅游产品。中美旅游年的启动，将进一步推进中国游客赴美旅游需求的增长，进而带动中美两国旅游软硬环境的建设，为游客往来提供更多便利。

    Marco Polo was from Venice, Italy. In 1271, at the age of 17, Marco went on a trip with his father and uncle to China. Today people often travel to different places around the world. But it was very hard for people from Europe to visit China then. After three and a half years, the Polos reached China in 1275.

    While he was there, Marco Polo worked for Kublai Khan, the emperor of China. He was able to learn and experience many things that were new to Europeans. In his diary, he wrote, "Kublai Khan's palace is the greatest I've ever seen. The streets of the new capital, Dadu, are so straight and so wide." Paper money also took him by surprise, since it was not yet in use in the West at that time. Homes were heated with "black stones… which burn like wood." Those stones were coal, and most of the Europeans knew little about it then.

After 17 years in China, Marco and his family finally returned to Venice. After he returned home, Marco completed a book called The Travels of Marco Polo, full of facts about his wonderful experiences in China.

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【提出问题】金属与盐酸反应剧烈程度受哪些因素的影响？

【做出猜想】a.可能与金属本身的性质有关；b.可能与盐酸的浓度有关。

【设计探究】实验所用金属均已用砂纸打磨。