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视图被用来对无权用户屏蔽数据。用户只能使用视图定义中的数据，而不能使用视图定义外的其他数据，从而保证了数据________。
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As the National Park Service celebrates its 100th anniversary(周年纪念),President Barack Obama has announced the establishment of one new national monument,and the expansion(扩大)of another.In Maine,more than 87,500 acres of forest will become government-protected parkland for the first time.In Hawaii,a national monument created by President George W.Bush in 2006 will expand to about 582,578 square miles,four times its current size. Obama has now created or enlarged 26 national monuments during his presidency.As a result,his administration says,Obama has protected more of the nation's land than any other president has.But some residents and officials,in both Maine and Hawaii,object to the plans.(78)They say their local economies depend on the use of these areas. In establishing this monument,Obama took the side of conservationists(自然资源保护者)who want laws to protect wild lands.Creating a national park usually requires the approval of Con-gress.But a 1906 federal law allows the president to establish national monuments on his own. The land's new status as a monument means that mining and drilling operations are forbidden there.(79)It may also severely limit activities such as logging,road-building,and hunting.Some of Maine's politicians who want to protect the state's logging industries say Obama should not have acted alone.They say Washington should not tell the states how to use their land,especially when people's jobs are at stake.Maine politician Susan Collins said the president should have listened to Maine lawmakers and residents,as well as to the U.S.Congress before making his decision. However,those who support the president's decision say the establishment of the new monu-ment will lead to new jobs through tourism.
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