单项选择题

The history of the American people is, (76) , the history of the movement of the American people. They moved from the colonies of the East Coast to the open space of the (77) . They moved from the country and the farm to the city. (78) , Americans have been moving from the cities to the suburbs.
Pioneer Americans began (79) from the East Coast to the West 250 years ago. They moved west for many reasons. (80) reason was that they could obtain (81) open space and land (82) farming. Americans liked large open spaces, and they liked the freedom and independence to (83) the land in their own way. Some of the land became farms. Important minerals were discovered in some areas, so some of the land became (84) . Other large areas became cattle ranches. There seemed to be enough land for everybody. But it was a diffieuh (85) of endless work and hardship.

85().