单选题   Para. 1 The rocky shorelines, shifting deserts and winding canyons of the country's 59 national parks have been hallmarks of American vacations for generations.
    Para. 2 But the number of park visitors has reached an unprecedented level, leaving many tourists frustrated and many environmentalists concerned about the toll of overcrowding.
    Para. 3 ①Zion is among the most visited parks in the system and is particularly prone to crowding because many of its most popular sites sit in a narrow six-mile canyon. ②So tiffs year, park managers announced they were considering a first for any national park: requiring reservations for entry.
    Para. 4 ①'We don't have a choice,' said Jack Burns, who has worked in Zion since 1982. ②'We have to do something. ③If this going to remain a place of special importance for generations, we have to do something now.'
    Para. 5 ①The National Park Service was created in 1916 to protect the country's growing system of parks and monuments. ②Its mandate is to conserve scenery and wildlife while also protecting visitor enjoyment for generations to come. ③For years, the lack of a reservation system for park entry aligned with the service's ethos of democracy and discovery: Anyone could come, pretty much anytime.
    Para. 6 ①But lately, both visitors and nature are suffering. ②Mr. Burns, who is on a team that is considering a reservation system, said some people showed up for a vacation they had planned for months, spent a day in the gridlock and turned around. ③Rangers, stressed by the frustrated masses, have started a monthly meeting to discuss 'visitor use' that some say has turned into a group-therapy session.
    Para. 7 ①And Zion's delicate desert ecosystem has been battered by tourists, some of whom wash diapers in the Virgin River, scratch their names into boulders and fly drone cameras through once quiet skies. ②The park has about 25 miles of developed trails. ③But over time, rangers have mapped about 600 miles of visitor-made paths, which damage vegetation and soil and take a toll on wildlife.
    Para. 8 ①The story is similar at parks from Yosemite in California to Acadia in Maine. ②And the crowding problem comes as the system faces the dual threat of a funding shortage and climate change.
    Para. 9 This summer, administrators at Zion submitted three proposed visitor plans to the public.
    Para. 10 ①One option would require people to make an online reservation before arrival, and would set a yet-to-be-specified limit on visitors. ②The second option would require reservations only for certain areas. ③The third option would be to make no changes.
    Para. 11 ①About 1,600 people sent in comments, and the park plans to send out a revised round of proposals for public review. ②Superintendent Jeff Bradybaugh will make the final decision.
    Para. 12 Some have expressed opposition to the reservation idea, including a group that founded the website stopzionreservations.org.
    Para. 13 ①Mr. Burns said he favored a reservation policy. ②He recalled the days when he would jump in a ear and pull up to parks across the West with no plans.
    Para. 14 ①'There is only one Zion National Park,' he said to those struggling to see a need for limiting access. ②'And it's sacred. ③Its beauty is sacred.'