课时作业29 A delicate world-（课时作业）【红对勾讲与练】2024版新高考英语大一轮复习全新方案（外研版）

选择性必修第二册　 3 课时作业 29　 A delicate world Ⅰ. 阅读理解 " (2022·吉林长春一模) The fertile land of the Nile Delta is being eroded (侵蚀) along Egypt􀆳s Mediterranean coast at an astonishing rate, in some parts estimated at 100 metres per year. In the past, land washed away from the coastline by the currents of the Mediterranean Sea used to be replaced by sediment (沉积物) brought down to the delta by the Nile River, but this is no longer happening. Up to now, people have blamed this loss of delta land on the two large Aswan Dams in the south of Egypt, which hold back almost all of the sediment that used to flow down the river. Before the dams were built, the Nile River flowed freely carrying huge quantities of sediment. But when the Aswan Dams were constructed to provide electricity and irrigation, and to protect the huge population centre of Cairo from annual flooding and drought, most of the sediment with its natural fertilizer accumulated up above the dam in the southern upstream half of Lake Nasser, instead of passing down to the delta. Now, however, there turns out to be more to the story. It appears that the sediment-free water picks up sand as it erodes the river bed and banks on the 800-kilometre trip to Cairo. Daniel Jean Stanley of the Smithsonian Institute noticed that water samples taken in Cairo indicated that the river sometimes carries more than 850 grams of sediment per cubic metre of water—almost half of what it carried before the dams were built. International environmental orga