【正确答案】[范文]
   With the progress of urbanization, an unprecedented number of people are living in big cities. The population of some megacities such as Beijing and Shanghai has exceeded 10 million. And the challenges faced by city dwellers are more and more discussed.
   To begin with, transport is one of the major challenges. When cities get bigger, people tend to live further away from their workplaces. It means that people need to commute a long distance between home and office. Crowded public transport or traffic jams during peak hours is obviously not a pleasant experience for commuters. Another big challenge is high housing prices and rent. The large population in cities drives up the housing prices as well as the rent. People have to spend much money in renting a place, despite the fact that they may earn more money in big cities. Many cannot afford to buy a house, which makes people anxious about their futures.
   To conclude, big city dwellers have to cope with various challenges and I think transport and housing issues are the most challenging for them.

【答案解析】 题目要求考生就“在大城市生活的挑战”进行论述。根据题目要求，可以采取以下布局：
   第一段：介绍与题目相关的社会背景，让题目更贴近生活。
   第二段：正文部分，提出自己的观点——生活在大城市将面临什么挑战。首先是交通问题：在大城市，人们的住处和工作场所离得比较远，通勤时间长，上下班高峰时段公共交通拥挤、交通堵塞，这种体验极为糟糕。其次是房价和租金问题：人们要支付高额的租金，根本买不起房，这使人们对未来感到焦虑。
   第三段：重申观点，总结全文。
   随着城市化的进程，居住在大城市的人口数量是史无前例的。北京、上海等一些特大城市的人口已超过1000万。城市居民面临的挑战正引发越来越多的讨论。
   首先，交通是主要的挑战之一。当城市扩张时，人们的住所往往远离他们的工作场所。这意味着人们需要在家庭和办公室之间通勤。对于上班族来说，经历高峰时段拥挤的公共交通、交通堵塞显然不是件愉快的事。另一个巨大的挑战是高房价和租金。城市人口众多，推高了房价和租金。尽管人们可以在大城市赚更多钱，但租房就已经是一大笔开销。很多人买不起自己的房子，这使他们对未来感到焦虑。
   总而言之，大城市的居民必须应对各种各样的挑战，我认为交通和住房问题对他们来说最具挑战性。