Recognizedasthelargestdesertintheworld，theSaharaDesertrunsacrossNorthAfrica．Exceptforanoccasionaloasis（绿洲），thisvastlandismainlymadeupofsand，stones，andwornoutmountains．Theburningsuncausesdaytimetemp

Question

Recognized as the largest desert in the world，the Sahara Desert runs across North Africa．Except for an occasional oasis（绿洲），this vast land is mainly made up of sand，stones，and worn out mountains．The burning sun causes daytime temperatures to rise to nearly 70degrees in the shade，and days without rain commonly last for years．
Paintings found on the walls of caves in the Sahara Desert suggest that a few thousand years ago，large quantities of plants grew there and covered the desert floor．Many curious and unusual insects，birds and animals got enough food that allowed them to grow and reproduce．At that time，huge river systems and many oases supported growing communities（社团，社区） where a large number of people lived．
Research scientists believe that the land became a desert for several reasons．For centuries people there have wandered（徘徊） from place to place in search of food，water，and grazing（吃草）land for their animals．These people have always considered the number of animals they have as a sign of wealth．The large herds（群）have been allowed to go freely and graze on desert plants and grass．Over time，large sections of land have been left uncovered．In addition to allowing over grazing，these people cut down whatever trees they could find and used them for firewood．The sand was unable to hold on to the great heat of the day，so nighttime temperatures often drop below freezing and nothing was left to hold the soil together．
Scientists have been studying different ways to bring back the green desert．Through research and experiments，they hope to be able to produce plants that will once again support the life there．Huge holes filled with much water lie under the desert surface．By making use of the sun's power，scientists in the Sahara have made experiments in which they got huge amount of electricity．This electricity was then used to operate drilling machines and pumps to pull the rainwater from the underground tanks．
Scientists have had some success turning this wasteland into useful farmland．Today the desert is dotted（点缀） with huge wheat fields watered by a system of pipes that carry water from the underground tanks．Farmers have also learnt that plants grow better if seeds are planted next to stones which could provide protection from the sun．In addition to that，greenhouses have been built to protect plants from the sunshine so that less water is needed．Another idea is to grow plants that can live on a diet of salt water，since the ocean is so near to the desert．
56．Which of the following is TRUE according to the passage？___
A．The desert is rich in beautiful color and scenery．
B．Allowing over grazing is the only reason to make the land became a desert．
C．The Sahara will one day become a beautiful garden．
D．Large river systems once supported many communities．
57．From the passage，we can infer that scientists are___．
A．pleased by the progress but do not have the money to continue
B．discouraged by the poor results of their experiments
C．hopeful about the chances of life coming back to the desert
D．troubled by the lack of water found underground
58．From paragraph 4and 5，we can know that___．
A．Animals have learnt to survive in the desert by lying next to rocks away from sunshine．
B．Through experiments，a desert may become a food-producing land．
C．Water supply will dry up before it can be used to grow crops．
D．Saltwater seeds will grow in the desert sand．
59．What is the main idea of this passage？___
A．Drilling machines help to water the desert floor and make plants and animals alive．
B．Scientists have been able to turn this large wasteland into a successful farming community．
C．So much soil has become sand that the desert will never be able to support life as it once did．
D．The desert no longer supports plenty of life，but researchers hope to change it with new scientific techniques．

Answer 1

56．D．细节理解题．根据第二段中的"At that time，huge river systems and many oases supported growing communities where a large number of people lived．"可知，巨大的水系曾经养活了很多的人，故D项正确．
 57．C．细节理解题．根据最后一段内容，特别是"Scientists have had some success turning this wasteland into useful farmland．"可知，科学家认为让撒哈拉沙漠重新富有生命是有希望的，故选C．
58．B．推理题，结合Through research and experiments，they hope to be able to produce plants that will once again support the life there可知经过试验，沙漠还可能会有新生命，故选B．
59．D．主旨大意题．根据文章内容，特别是最后一段内容Scientists have had some success turning this wasteland into useful farmland可知，本文主要介绍了虽然撒哈拉沙漠现在是不毛之地，但是科学家们正努力让它重新富有生命，故D项正确．