题目内容：
请根据短文内容，回答题。The history of the American people is， ____51____ ，the history of the movement of the American people．They moved from the colonies of the East Coast to the open space of the ____52____ ．They moved from the country and the farm to the city．____53____，Americans have been moving from the cities to the suburbs．
Pioneer Americans began ____54____ from the East Coast to the West 250 years ago．They moved west for many reasons． ____55____ reason was that they could obtain ____56____ .Open space and land ____57____ farming．Americans liked large open spaces，and they liked the freedom and independence to ____58____ 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 ____59____ ．Other large areas became cattle ranches．There seemed to be enough land for everybody．But it was a difficult ____60____ of endless work and hardship．
________ A．with part
B．of part
C．in part
D．on part
参考答案：
答案解析：