Rainfallis not completely absent indesertareas, but it is highlyvariable. Anannualrainfallof four inches is often used todefinethe limits of adesert. Theimpactofrainfallupon the surface water andgroundwaterresources of thedesertis greatly influenced by landforms. Flats and depressions where water cancollectarecommonfeatures, but they make up only a small part of thelandscape.

Aridlands, surprisingly,containsome of the world’s largest river systems, such as the Murray-Darling in Australia, the Rio Grande in North America, the Indus in Asia, and the Nile in Africa. These rivers and river systems are known as "exogenous" because their sources lie outside thearidzone. They arevitalfor sustaining life in some of the driest parts of the world. For centuries, theannualfloods of the Nile,Tigris, andEuphrates, for example, have broughtfertilesilts and water to the inhabitants of theirlowervalleys. Today, river discharges are increasingly controlled by human intervention, creating a need for international river-basin agreements. The filling of the Ataturk and other dams inTurkeyhasdrasticallyreduced flows in theEuphrates, with potentially serious consequences for Syria and Iraq.

The flow of exogenous rivers varies with theseason. Thedesertsections of long riversrespondseveral months after rain has fallen outside thedesert, so thatpeakflows may be in the dryseason. This is useful forirrigation, but the high temperatures, low humidities, and different day lengths of the dryseason, compared to the normal growingseason, can present difficulties with some crops.

Regularly flowing rivers and streams thatoriginatewithinaridlands are known as "endogenous." These are generally fed bygroundwatersprings, and manyissuefromlimestonemassifs, such as the Atlas Mountains in Morocco. Basaltic rocks also support springs,notablyat the Jabal Al-Arab on the Jordan-Syriaborder. Endogenous rivers often do notreachthe sea butdraininto inland basins, where the water evaporates or is lost in the ground. Mostdesertstreambeds arenormallydry, but they occasionally receive large flows of water andsediment.

Desertscontainlarge amounts ofgroundwaterwhen compared to the amounts they hold in surface stores such as lakes and rivers. But only a smallfractionofgroundwaterenters the hydrologicalcycle—feeding the flows of streams, maintaining lake levels, and being recharged (or refilled)throughsurface flows and rainwater. In recent years,groundwaterhas become an increasingly importantsourceof freshwater fordesertdwellers. The United Nations Environment Program and the World Bank have funded attempts tosurveythegroundwaterresources ofaridlands and to developappropriateextraction techniques. Such programs are much needed because in manyaridlands there is only avagueidea of theextentofgroundwaterresources. It is known, however, that thedistributionofgroundwaterisuneven, and that much of it lies at great depths.

Groundwateris stored in theporespaces and joints of rocks andunconsolidated(unsolidified) sediments or in the openings widenedthroughfractures andweathering. The water-saturated rock orsedimentis known as an "aquifer". Because they areporous,sedimentaryrocks, such as sandstones and conglomerates, are importantpotentialsources ofgroundwater. Large quantities of water may also be stored in limestones when joints and cracks have been enlarged to form cavities. Mostlimestoneand sandstone aquifers are deep andextensivebut maycontaingroundwaters that are not being recharged. Mostshallowaquifers in sand andgraveldeposits produceloweryields, but they can be rapidly recharged. Some deep aquifers are known as "fossilwaters. Theterm"fossil" describes water that has been present for several thousand years. These aquifers became saturated more than 10,000 years ago and are no longer being recharged.

Water does notremainimmobile in anaquiferbut canseepout at springs orleakinto other aquifers. Therateof movement may be very slow: in the Indusplain, the movement of saline (salty) groundwaters has still not reachedequilibriumafter 70 years of being tapped. Themineralcontentofgroundwaternormallyincreases with the depth, butevenquiteshallowaquifers can be highly saline.

Questions:
question_stem: Which of the following statements about annual rainfall can be inferred from paragraph 1?
choices: tag: A
text: Flat desert areas receive more annual rainfall than desert areas with mountains.

tag: B
text: Areas that receive more than four inches of rain per year are not considered deserts.

tag: C
text: Many areas receive less than four inches of annual rainfall, but only a few are deserts.

tag: D
text: Annual rainfall has no impact on the groundwater resources of desert areas.
answer_key: B
explanation: B 以 annual rainfall 做关键词定位至第二句，说年降雨量少于4 inch 的地方被认为是沙漠，推断出相反的一面是年降雨量大于4 inch 的地方不是沙漠，也就是 B。

question_stem: The word “drastically” in the passage is closest in meaning to
choices: tag: A
text: obviously

tag: B
text: unfortunately

tag: C
text: rapidly

tag: D
text: severely
answer_key: D
explanation: D drastically: 彻底地，激烈地。A 是明显地；B 是不幸地；C 是快速地；D 是剧烈地。所以 D 的 severely 正确。

question_stem: In paragraph 2, why does the author mention the Ataturk and other dams in Turkey?
choices: tag: A
text: To contrast the Euphrates River with other exogenous rivers

tag: B
text: To illustrate the technological advances in dam building

tag: C
text: To argue that dams should not be built on the Euphrates River

tag: D
text: To support the idea that international river-basin agreements are needed
answer_key: D
explanation: 功能目的题，两个细节所在的句子只是单纯的说了一个例子，往前看，说河水流量越来越多地被人控制，使得需要有一个 agreements，所以答案是 D，需要 agreement。

question_stem: According to paragraph 2, which of the following is true of the Nile River?
choices: tag: A
text: The Nile's flow in its desert sections is at its lowest during the dry season

tag: B
text: The Nile's sources are located in one of the most arid zones of the world

tag: C
text: The Nile's annual floods bring fertile silts and water to its lower valley

tag: D
text: The Nile's periodic flooding hinders the growth of some crops
answer_key: C
explanation: C 以 Nile 做关键词定位至第一句和第四句，第一句中尼罗河只是个例子，所以答案在第四句，说尼罗河泛滥给 valley 带去 silt 和 water，与 C 完全一样，所以答案是 C。

question_stem: The word “dwellers” in the passage is closest in meaning to
choices: tag: A
text: settlements

tag: B
text: farmers

tag: C
text: tribes

tag: D
text: inhabitants
answer_key: D
explanation: D dwell: 定居。所以 dweller 是居民之意。A 是定居；B 是农民；C 是部落；D 是居民。所以 D 的 inhabitants 正确。

question_stem: Paragraph 5 supports all of the following statements about the groundwater In deserts EXCEPT:
choices: tag: A
text: The groundwater is consistently found just below the surface

tag: B
text: A small part of the groundwater helps maintain lake levels

tag: C
text: Most of the groundwater is not recharged through surface water

tag: D
text: The groundwater is increasingly used as a source of freshwater
answer_key: A
explanation: A EXCEPT 题，排除法。A 在原文中没有对应，错，选；B 的 lake level 做关键词定位至第二句，small fraction 与 small part 同义替换，正确，不选；C 的 surface water 与第二句的 surface flow 同义替换，正确，不选；D 的 freshwater 做关键词定位至第三句，正确，不选。

question_stem: The word “fractures” in the passage is closest in meaning to
choices: tag: A
text: streams

tag: B
text: cracks

tag: C
text: storms

tag: D
text: earthquakes
answer_key: B
explanation: B fracture: 断裂，裂隙，裂缝。A 是溪流；B 是裂缝；C 是暴风；D 是地震。所以 B 的 crack 正确。

question_stem: According to paragraph 6, which of the following statements about aquifers in deserts is true?
choices: tag: A
text: Water from limestone and sandstone aquifers is generally better to drink than water from sand and gravel aquifers

tag: B
text: Sand and gravel aquifers tend to contain less groundwater than limestone or sandstone aquifers

tag: C
text: Groundwater in deep aquifers is more likely to be recharged than groundwater in shallow aquifers

tag: D
text: Sedimentary rocks, because they are porous, are not capable of storing large amounts of groundwater
answer_key: B
explanation: B 此题用 auifer 做关键词定位的话可能需要读较多文章，使用排除法较快。A 的 limestone 做关键词定位至第五句，但这句完全没说 drink 的事儿，所以 A 错；B 的 sand and gravel 做关键词定位至倒数第四句，说 sand and aquifer 的产水量低，但更容易 recharge，前句说到 limestone 和 sandstone，说明高的是这两种，所以 B 正确，同时 C 说反；D 的 sedimentary rocks 做关键词定位至第三句，应该是能储存，选项说反，错。

question_stem: According to paragraph 6, the aquifers called fossil waters
choices: tag: A
text: contain fossils that are thousands of years old

tag: B
text: took more than 10,000 years to become saturated with water

tag: C
text: have not gained or lost any water for thousands of years

tag: D
text: have been collecting water for the past 10,000 years
answer_key: C
explanation: C 以 fossil waters 做关键词定位至倒数三句，说含有 fossil water 的含水层早在千年之前就 saturated，不在 recharge 了，所以答案是 C；这句话说10000年前就 saturated 了，所以 B 的一万年才变 saturated 和 D 的聚集了一万年的水都不对；A 完全不靠谱。

question_stem: The word “immobile” in the passage is closest in meaning to
choices: tag: A
text: enclosed

tag: B
text: permanent

tag: C
text: motionless

tag: D
text: intact
answer_key: C
explanation: C immobile: 不动的，不变的。A 是封闭的；B 是永久的；C 是不动的；D 是完整的。所以 C 的 motionless 正确。

question_stem: The passage supports which of the following statements about water in the desert?
choices: tag: A
text: The most visible forms of water are not the most widespread forms of water in the desert.

tag: B
text: Groundwater in the desert cannot become a source of drinking water but can be used for irrigation.

tag: C
text: Most of the water in the desert is contained in shallow aquifers that are being rapidly recharged.

tag: D
text: Desert areas that lack endogenous or exogenous rivers and streams cannot support life.
answer_key: A
explanation: A 问整个 passage，所以排除法最好，而且应该关注各段的开头。A 的信息在第五段的开头，说沙漠的水量比河流和湖泊大，而河流和湖泊是最常见的水存在的形式，但却不是最多的，所以 A 正确；B 错，原文第三段说到能够灌溉，但没说不能喝，错；C 的 rapidly recharged 明显和第六段第五句不 recharge 相反；D 原文没说。