SHE IS ALWAYSTACTFULWHEN SHE DEALS WITH ANGRY STUDENTS.A.STRICT B.FIRM...

Câu 54:She is alwaystactfulwhen she deals with angry students.A.strict B.firm C.discourteous D.outspokenRead the following passage and mark the letter A, B, C or D on your answer sheet to indicate the correctanswer to each of the questions.Early peoples had no need of engineering works to supply their water. Hunters and nomads camped nearnatural sources of fresh water, and populations were so sparse that pollution of the water supply was not aserious problem. After community life developed and agricultural villages became urban centres, the problem ofsupplying water became important for inhabitants of a city, as well as for irrigation of the farms surrounding thecity. Irrigation works were known in prehistoric times, and before 2000 BC the rulers of Babylonia and Egyptconstructed systems of dams and canals toimpoundthe flood waters of the Euphrates and Nile rivers,controlling floods and providing irrigation water throughout the dry season. Such irrigation canals also suppliedwater for domestic purposes. The first people to consider the sanitation of their water supply were the ancientRomans, who constructed a vast system of aqueducts to bring the clean waters of the Apennine Mountains intothe city and built basins and filters along thesemainsto ensure the clarity of the water. The construction of suchextensive water-supply systems declined when the Roman Empire disintegrated, and for several centuries localsprings and wells formed the main source of domestic and industrial water.The invention of the force pump in England in the middle of the 16th century greatly extended thepossibilities of development of water-supply systems. In London, the first pumping waterworks was completedin 1562; it pumped river water to a reservoir about 37 m above the level of the River Thames and from thereservoir the water was distributed by gravity, through lead pipes, to buildings in thevicinity.Increased per-capita demand has coincided with water shortages in many countries. Southeast England,for example, receives only 14 per cent of Britain's rainfall, has 30 per cent of its population, and hasexperienced declining winter rainfall since the 1980s.In recent years a great deal of interest has been shown in the conversion of seawater to fresh water toprovide drinking water for very dry areas, such as the Middle East. Several different processes, includingdistillation, electrodialysis, reverse osmosis, and direct-freeze evaporation, have been developed for thispurpose. Some of these processes have been used in large facilities in the United States. Although theseprocesses are successful, the cost of treating seawater is much higher than that for treating fresh water.