Since the majority of Indian reservations are in the arid West, it is understandable that water has been a central environmental issue. By 1900, whites actively competed with Indians for this (47)______ resource. At one Indian Reservation in Montana, white settlers diverted (使转向) water from the Milk River. When ordered to stop, they argued that the Indians had not made prior appropriation use. In 1908 the Supreme Court ruled in Winters v. United States that in establishing reservations, Congress implied and reserved the priority water rights necessary for (48)______ and future use. Encouraged by the Winters decision, the Indian Bureau used Indian funds to construct elaborate irrigation (灌溉) systems to protect Indian water and improve the (49)______ potential of the allotted land. Irrigation promised to change the landscape and increase Indian self-sufficiency, but the systems suffered from poor construction, improper use and (50)______, and often ended up in the hands of white (51)______ who bought up the best Indian lands. Twentieth-century big dam projects also had unforeseen consequences for Indians and their lands. As part of the Newlands Project in 1905, the government dammed and diverted the Truckee River for white irrigation. The diversion of water nearly killed Pyramid Lake. During the New Deal, the government completed numerous, if not always successful, water projects on western reservations. Since the 1930s, dams on the Columbia River have prevented the migration of some fishes, flooded sacred sites and Indian fisheries (渔场), and (52)______ upstream spawning grounds. On the Missouri River, the Pick-Sloan Plan for damming and flood control proved (53)______ for Indians of the nearby reservations. They watched the waters cover rich agricultural lands, villages, and sacred sites in the name of (54)______. Similar things happened in the 1960s and 1970s. Today, these dams raise important environmental issues of water flow through reservations, of aquatic (水生的) species (55)______ and Indian fishing rights, and the ownership and sale of water. While the Winters Doctrine assured Indian water rights, it never quantified those rights. The issue of how much water tribes can legitimately use and sell has become (56)______ in the arid West, especially for tribes in states member to the Colorado River Compact. Word BankA) settlers B) critical C) progressD) beneficial E) ruined F) presentG) function H) scarce I) termJ) disastrous K) preservation L) agriculturalM) maintenance N) appropriate O) decisions