​SPEED READING 

Complete the following sentence with the proper form of the word in the bracket.

     Yellowstone National Park, established by the U. S. Congress as a national park on March 1,1872, is located primarily in the U. S. state of Wyoming, though it also extends into Montana and Idaho. The park was the first of its kind, and is known for its wildlife and its many geothermal (地热的) features, especially Old Faithful Geyser, one of the most popular features in the park. It has many types of ecosystems, but the subalpine (亚高山带的)forest is dominant.
     American Indians have lived in the Yellowstone region for at least 11,000 years. The region was bypassed during the Lewis and Clark Expedition in the early 1800s. Aside from visits by mountain men during the early to mid 1800s, organized exploration did not begin until the late 1860s. The U. S. Army was commissioned to oversee the park just after its establishment. In 1917 administration of the park was transferred to the National Park Service, which had been created the previous year. Hundreds of structures have been built and are protected for their architectural and historical significance, and researchers have examined more than 1,000 archaeological sites.
     Yellowstone National Park spans an area of 3,468 square miles, comprising lakes, canyons, rivers and mountain ranges. Yellowstone Lake is one of the largest high-altitude lakes in North America and is centered over the Yellowstone Caldera, the largest super-volcano on the continent. The caldera is considered an active volcano；it has erupted with tremendous force several times in the last two million years. Half of the world's geothermal features are in Yellowstone, fueled by ongoing volcanic activities. Lava flows and rocks from volcanic eruptions cover most of the land area of Yellowstone. The park is the centerpiece of the Greater Yellowstone Ecosystem, the largest remaining, nearly-intact ecosystem in the Earth's northern temperate zone.
     Hundreds of species of mammals, birds, fish and reptiles have been documented, including several that are either endangered or threatened. There are almost 60 species of mammals in the park. Apart from wildlife, there are 1,700 species of trees and other plants native to the park. Another 170 species are considered to be exotic species and are non-native.
     As one of the most popular national parks in the United States, Yellowstone provides numerous recreational opportunities, including hiking, camping, boating, fishing and sightseeing. Paved roads provide close access to the major geothermal areas as well as some of the lakes and waterfalls. Since the mid 1960s, at least 2 million tourists have visited the park almost every year. Nine hotels and lodges, with a total of 2,238 rooms and cabins, are available to tourists from all over the world. Hundreds of employees work either permanently or seasonally for the National Park Service.