2017届四川省青川县高考英语一轮复习阅读理解基础选练：6（含答案）_高考复习指南

2017届四川省青川县高考英语一轮复习阅读理解基础选练：6（含答案）

　　Research scientists believe that the land became a desert for several reasons. For centuries people there have wandered 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. It is considered more important to have 100 sick and starving animals than 15 healthy ones. 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 overgrazing, 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 nightting 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. Scientists believe this rainwater simply flew down through the sand over hundreds of years and collected in the big, rocky holding tanks. 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. By drilling the hole one mile deep into the floor of the desert, one machine was able to recover more than 80 gallons of ice—cold water each second, or 288,000 gallons per hour.