5, 159 & 173

　　5. The following appeared in a letter to the editor of the Balmer Island Gazette.

　　北京新东方 万炜

　　"On Balmer Island, where mopeds serve as a popular form of transportation, the population increases to 100,000 during the summer months. To reduce the number of accidents involving mopeds and pedestrians, the town council of Balmer Island should limit the number of mopeds rented by the island's moped rental companies from 50 per day to 25 per day during the summer season. By limiting the number of rentals, the town council will attain the 50 percent annual reduction in moped accidents that was achieved last year on the neighboring island of Seaville, when Seaville's town council enforced similar limits on moped rentals."

　　Write a response in which you discuss what questions would need to be answered in order to decide whether the recommendation is likely to have the predicted result. Be sure to explain how the answers to these questions would help to evaluate the recommendation.

　　步骤：夏天人口增多 + 摩托车是主要交通工具 → 到了夏天摩托车引起的事故会增多

　　假设：夏天增多的人口会造成严重的摩托车问题

　　反例：城市交通秩序好，摩托车司机都很职业，很守规矩，历年来都没出什么事故

　　补充证据：往年夏天的摩托车事故率

　　步骤：SV执行了摩托车禁令 + 之后SV的事故减少50% → 是禁令减少的事故

　　假设：没有它因

　　反例：道路拓宽;司机培训更严格;交通法规更严格;警察多了

　　补充证据：……

　　步骤：SV成功 → BI成功

　　假设：两城的租赁摩托车都是主要摩托车的来源;过去两城摩托车都能够租出去

　　反例：SV的摩托车都是租的，但是BI的摩托车都是私家的;SV的都租出去了，但是BI的本来就租不到每天25辆

　　补充证据：两城摩托车的主要来源;既往摩托车每天实际租赁量

　　步骤：BI成功减少夏天的事故→全年事故的减少

　　假设：夏天的事故是全年事故的主要来源

　　反例：夏天路况好，人多不是事故的来源。全年事故主要来源于冬天路面结冰。而冬天车辆没减少，所以事故不会减少50%

　　证据：全年的事故数量变化表。

编辑：张雨

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