填空题

In the past, the Park Service focused on making the big scenic parks more 【21】 and comfortable for tourists. Roads were paved to allow "windshield visitors" to experience the grandeur of nature without leaving their cars, and a 【22】 number of hotels and grocery stores were permitted to open 【23】 the park boundaries. Now this trend is changing. Plans have been made to 【24】 the parks to their natural condition as much as possible. The objective of such a move would be to secure the preservation of the parks for future generations, 【25】 allowing present-day visitors to experience pure wilderness, 【26】 from any obvious signs of civilization ― an opportunity which is quickly disappearing in the twentieth century. 【27】 plans call only 【28】 a reduction in the number of cars 【29】 into the parks each day, but 【30】 , tourists may have to leave their cars at the gates and then dither visit the park on foot 【31】 use park 【32】 . 【33】 , stores and hotels may no longer be allowed within park boundaries and even the number of campgrounds may be restricted. Denali National Park in Alaska serves as an excellent 【34】 for this new type of park, one which has been changed only slightly from its 【35】 state. There is only one road, unpaved in 【36】 ,which cross 【37】 Denali. As car traffic is strictly limited, many visitors experience the magnificent 【38】 and wildlife from a park bus. There are no hotels or stores and only seven campgrounds within Denali’’s 3,000 square miles. This 【39】 isolation offers backpackers, canoeists, and other sport enthusiasts a 【40】 physical and psychological challenge.