Fill in each gap with ONE suitable word tocomplete the passage

Fill in each gap with ONE suitable word tocomplete the passage.

The national park movement began in the United States in 1870. (1)………. a team of explorers suggested that part of the Yellowstone River region (2) ………..set aside in order to protect its geothermal features, wildlife, forest, and exceptional scenery for the benefit of future (3)………...., Congress responded (4)…………. creating Yellowstone National Park, the world’s first, in 1872. The idea proved popular, and the number of national parks in the country (5)…………. rapidly, new parks being set (6)…………… by presidential proclamation and sometimes (7)………… the result of gifts by states of the union or by individuals. Administration of this increasingly complex system (8)………. in the hands of the U. S Army for thirty years (9)………. 1886, but then Congress created the National Park Service as part of the Department of the Interior to oversee (10)……………
Today, in (11)……………. to what might be thought of as typical national parks, the Service also manages of historic interest, hiking trail, seashores, rivers, reserves of scientific interest, and memorials. In all, more than 300 entities are involved, (12) ……………over 32 million hectares. Each unit is directed by a superintendent (13)………….. is responsible
for all aspects of the operation. Staff (14) …………..administrative personnel and, (15)………. to the nature of the unit, park rangers, naturalists, historians, and maintenance workers. Perhaps unexpectedly, the Statue of Liberty and (16)……….. White House both fall within the system. It is sites such as these which help account (17)………. the extraordinary number of visitors, now totaling some 400 million annually. To serve such large (18)…………, guest facilities are offered at every site, (19)…………….. may include hotels, restaurants, gas stations, and transportation, systems. All (20)………….. are operated by private concessionaires, who must observe specific regulations imposed by the Federal Government.