小站备考
托福
托福阅读
Official48阅读真题

OFFICIAL48 Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points. Drag your answer choices to the spaces where they belong. To remove an answer choice, click on it. Cities are generally warmer than the surrounding countryside, a phenomenon known as the urban heat island

展开
Climate and Urban Development
Tip:单击查看句义;划选/双击查生词
For more than a hundred years, it has been known that cities are generally warmer than surrounding rural areas. This region of city warmth, known as the urban heat island, can influence the concentration of air pollution. However, before we look at its influence, let’s see how the heat island actually forms.

The urban heat island is due to industrial and urban development. In rural areas, a large part of the incoming solar energy is used in evaporating water from vegetation and soil. In cities, where less vegetation and exposed soil exist, the majority of the Sun’s energy is absorbed by urban structures and asphalt. Hence, during warm daylight hours, less evaporative cooling in cities allows surface temperatures to rise higher than in rural areas. The cause of the urban heat island is quite involved. Depending on the location, time of year, and time of day, any or all of the following differences between cities and their surroundings can be important: albedo (reflectivity of the surface), surface roughness, emissions of heat, emissions of moisture, and emissions of particles that affect net radiation and the growth of cloud droplets.

At night, the solar energy (stored as vast quantities of heat in city buildings and roads) is slowly released into the city air. Additional city heat is given off at night (and during the day) by vehicles and factories, as well as by industrial and domestic heating and cooling units. The release of heat energy is retarded by the tall vertical city walls that do not allow infrared radiation to escape as readily as does the relatively level surface of the surrounding countryside. The slow release of heat tends to keep nighttime city temperatures higher than those of the faster-cooling rural areas. Overall, the heat island is strongest (1) at night when compensating sunlight is absent; (2) during the winter, when nights are longer and there is more heat generated in the city; and (3) when the region is dominated by a high-pressure area with light winds, clear skies, and less humid air. Over time, increasing urban heat islands affect climatological temperature records, producing artificial warming in climatic records taken in cities. This warming, therefore, must be accounted for in interpreting climate change over the past century.

The constant outpouring of pollutants into the environment may influence the climate of the city. Certain particles reflect solar radiation, thereby reducing the sunlight that reaches the surface. Some particles serve as nuclei upon which water and ice form. Water vapor condenses onto these particles when the relative humidity is as low as 70 percent, forming haze that greatly reduces visibility. Moreover, the added nuclei increase the frequency of city fog.

Studies suggest that precipitation may be greater in cities than in the surrounding countryside; this phenomenon may be due in part to the increased roughness of city terrain, brought on by large structures that cause surface air to slow and gradually converge. This piling up of air over the city then slowly rises, much like toothpaste does when its tube is squeezed. At the same time, city heat warms the surface air, making it more unstable, which enhances risings air motions, which, in turn, aids in forming clouds and thunderstorms. This process helps explain why both tend to be more frequent over cities.

On clear still nights when the heat island is pronounced, a small thermal low-pressure area forms over the city. Sometimes a light breeze—called a country breeze—blows from the countryside into the city. If there are major industrial areas along the outskirts, pollutants are carried into the heart of town, where they tend to concentrate. Such an event is especially probable if vertical mixing and dispersion of pollutants are inhibited. Pollutants from urban areas may even affect the weather downwind from them.

14.Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points. Drag your answer choices to the spaces where they belong. To remove an answer choice, click on it. Cities are generally warmer than the surrounding countryside, a phenomenon known as the urban heat island

A.In the countryside, much solar energy is used in evaporation, but in the city this energy builds up as heat

B.Increased industrial and urban development has also increased average levels of humidity over the last century

C.Pollution from cars and factories helps increase the amounts of fog and precipitation that occur in cities

D.The urban heat island is strongest in the summer, when the days are long and the sunlight is intense

E.Heat and air are trapped in the irregular spaces between buildings, which creates the atmospheric conditions that result in storms and winds

F.Country breezes blow pollutants put from the cities into the surrounding countryside

你的答案:
正确答案:ACE
题目解析:
 后才能查看题目解析,还没有账号? 马上注册
【题目翻译】 问题:方向:一个介绍性的句子提供了一个简短的总结的下面。通过选择三个选项来完成总结,这三个选项表达了文章中最重要的观点。有些句子不属于总结,因为它们表达的是文章中没有提到的观点,或者是文章中的次要观点。这个问题值两分。将您的答案选项拖到它们所属的位置。要删除答案选项,单击它。城市通常比周围的乡村更温暖,这种现象被称为城市热岛 选项: A:在农村,太阳能是用于蒸发,但在城市这个能量积聚的热量 B:增加了工业和城市发展也增加湿度在上个世纪的平均水平 C:汽车尾气和工厂帮助增加大量的雾和降水发生在城市 D:在夏季城市热岛是最强的,当日子长,阳光强烈 艾凡:热量和空气被困在不规则的建筑物之间的空间,形成大气条件,导致暴雨和大风 F:国家微风吹污染物从城市周边农村地区 【判定题型】:根据问题的提问方式和6选3的作答方式可以确定该题目为概要小结题。 【选项定位及分析】 A选项:文章首先介绍太阳能在农村都用于蒸发水分,而在城市都储存为热,对应选项A中:In the countryside, much solar energy is used in evaporation, but in the city this energy builds up as heat,故选A选项。 C选项:文章然后介绍污染物会让城市有更多烟雾和降雨,对应许选项C中:Pollution from cars and factories helps increase the amounts of fog and precipitation that occur in cities,故排除。 E选项:文章最后介绍压强差导致风暴,对应选项E中:Heat and air are trapped in the irregular spaces between buildings, which creates the atmospheric conditions that result in storms and winds。故选E选项。 D选项:文章没有提到湿度的升降,选项B错在humidity。文章说冬天城市热岛效应更为明显,选项D错在summer。故排除。 F选项:文章说污染物从郊区走向城市,选项F错在from cities into … countryside。故排除。

学习页面

Medi

terr

anean

加强 + 政府 + 名词后缀

加强的政府——管理

原文例句

加入生词

本文生词 0

色块区域是你收藏过的生词;

查询次数越多,颜色越深哦~

显示文中生词

登录后才能收藏生词哦,现在登录注册>

本文重点词 45

文中加粗单词为本文重点词;

根据词频与核心词范围精心挑选,托福考试必掌握词汇。

显示文中重点词
学习本文词汇

文中划选/双击的生词、加粗重点词已收纳至词盒

可随时点击词盒查看哦~

只有在词句精学模式下才能开启词盒功能哦~

我知道了

词盒
收藏
笔记
我的笔记
5000
保存
反馈