Ctchujxfhhjb Man and most animals need a constant supply of water to live. Farmers need water for their crops.,Hydroelectric dams hold back needed water and provide power for homes and industries.,Trees and grass, and other plant life play an important part in the natural circulation of water, thus,help conserve it. Without plants, most water would run off as soon as it falls, taking away valuable soil.,Rapid runoff would cause frequent floods, and leave little water during dry seasons.,Nature has many ways of conserving and controlling water. But man often upsets the water,balance in his desire to grow more crops. He drains ponds, swamps and wet land. He ploughs under the,natural soil, cuts timber, and dredges and straightens streams. These changes reduce natural storage of,water and speed runoff.,Water can be held on the land by planting vegetation. Forests and grass should be planted where,there are no natural growths. Dams built across rivers help hold back the water. Reservoirs behind the,dams store water during wet seasons for use in dry seasons. Dams help prevent floods by controlling the,flow of water.,Note: to dredge = to make a river deeper,21. What is the topic of the passage?,A. Water circulation B. Water conservation C. Controlling water D. Use of water,22. What is the consequence of having no plants on land?,A. no water B. frequent floods C. dry crops D. valuable soil,23. Which is one of the ways that men do to affect the water balance?,A. shortening streams B. cutting down trees,C. preserving water D. protecting ponds and swamps,24. What is NOT a natural way of conserving and controlling water?,A. ponds B. streams C. swamps D. reservoirs,25. What do people use reservoirs for?,A. growing plants B. building dams C. storing water D. preventing floods,Rewrite the sentences as directed

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21. B. Water conservation

22. B

23. B. cutting down trees

24. D. reservoirs

25. C. storing water - trữ nước