49. What is the main idea of this passage? 這段話的主要思想是什麼？ (A)Someday most glaciers in the world will disappear completely. 有一天，大多數在世界上的冰川將完全消失。 (B)Melting glaciers provide water for irrigation, drinking, and transportation. 冰川融化水用於灌溉，飲用，運輸。 (C)Temperature change and a lack of snow causes the decrease of glaciers. 溫度變化和缺乏雪導致冰川減少。 (D)The melting of glaciers is potentially disastrous to human beings. 冰川的融化是對人類潛在的災難性的。 第47題至第50題為題組 The melting waters of the Ruwenzori Mountains feed the headwaters of the Nile. Here, for hundreds of thousands of years, people have depended on the river for basic necessities: water, transportation, farming, and fishing. Now, the glaciers of the Ruwenzori are melting so rapidly that they will soon disappear. Within the next twenty or thirty years, most glaciers in Africa and South America will vanish completely. The shrinking of the world’s glaciers will have massive consequences for communities that depend on ice melt. In the short-term, these consequences may appear beneficial. For example, extra water from glaciers means that hydroelectric dams will run at maximum power. In the long run, however, the melting of earth’s glaciers could be catastrophic. Today’s extra hydroelectric power has been stolen from the future. Communities with ample power now may have none after the glaciers have melted, and the loss of ice will increase sea levels worldwide. Temperature change and a lack of snow is causing the retreat of the glaciers. Glaciers are no longer getting built up during the snowy winter months, so they are no longer able to maintain their size over the long run. Unless there are some changes in the current rate of global warming, the glaciers are essentially doomed.What is the main idea of this passage? 47 What does the word “beneficial” mean in this passage? A. Helpful B. Worthless C. Dangerous D. Unbelievable 48 Which of the following descrXXXiptions of glaciers is true? A. Glaciers are the main water source for the Nile. B. Melting glaciers may help hydroelectric dams run at maximum power for a long time. C. As temperature increases, glaciers are getting built up. D. Melting glaciers will result in the decline of sea levels. 49 What is the main idea of this ..