托福閱讀真題Official 48 Passage 3（五）

托福閱讀真題Official 48 Passage 3（五）

Climate and Urban Development

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 air pressure(atmospheric pressure)is the pressure exerted by the mass of air above a given place 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 rising 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.

Question 9 of 14

Why does the author mention“toothpaste”being squeezed from a tube?

A.To compare the movement of toothpaste from a tube to the movement of precipitation from clouds

B.To suggest that the process of cloud formation is a simple,everyday experience

C.To help the reader visualize the process of air movement over a city

D.To contrast the slow rising of air currents with the rapid squeezing of toothpaste

正確答案：C

題目詳解

題型分類：修辭目的題

題干分析：考察句子之間的關(guān)系。原文中說像擠牙膏一樣來比喻空氣緩慢的移動。

選項分析：

C選項：幫助讀者想象城市上空空氣流動的過程。

A選項：將牙膏在管內(nèi)的運(yùn)動與從云層中的降雨相比較，錯誤，不是來和降雨發(fā)生比較的。

B選項：表明云彩的形成過程很簡單、很常見，錯誤。

D選項：將空氣流的緩慢上升與快速擠壓牙膏相對比，錯誤，是慢慢移動。

Question 10 of 14

The word“both”in the passage refers to

A.piling up and warming of air

B.clouds and thunderstorms

C.warm surface air and rising air motions

D.heat and instability

正確答案：B

題目詳解

題型分類：指代題

題干分析：指代詞一般指代前方的對應(yīng)內(nèi)容

原文定位：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.與此同時，城市熱量使表面的空氣變暖,使之更不穩(wěn)定，增強(qiáng)了上升的空氣運(yùn)動,這反過來，有助于形成云層和雷暴。這個過程幫助解釋為什么這兩者在城市上空更容易發(fā)生。

選項分析：

B選項clouds and thunderstorms根據(jù)句間指代的就近原則和語義原則，指代的內(nèi)容因為云層和雷暴，正確。

A選項piling up and warming of air前文沒有提到，錯誤。

C選項warm surface air and rising air motions，前文有提到，但是不是this process的指代內(nèi)容，錯誤。

D選項heat and instability前文沒提，錯誤。

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