Although parks of all sizes and types exist at any level, the national parks, in particular, tend 41 (catch) our attention because of their large size and variety. They are 42 (treasure) of American heritage (遗产). How did the national park system come about? On a cool, starry night in mid-September 1870, four men relaxed before a campfire along the Firehole River in 43 is now northwestern Wyoming. They 44(be) part of a 15-member exploring party that had spent almost five awesome weeks in witness of the natural beauties there.
What should 45(do) with such a beautiful place? They wondered out loud. This area, with 46 (it) unique and breathtaking natural beauty, must be well preserved 47 all people of the nation to enjoy — as a national park. They all agreed and vowed (承诺) to promote the idea at the 48 (complete) of their journey. Their promotional work paid off. Two years later, 18 years before Wyoming became a state, Yellowstone became the first national park in the United States and the world. Yellowstone was the 49 (large) United States national park — 2.2 million acres — until Wrangell-Saint Elias in southern Alaska, _50_ became a national monument in 1978, took the honors as a national park in 1980 with 12.3 million acres.

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