If by "suburb" is meant an urban margin that grows more rapidly than its already developed interior, the process of suburbanization began during the appearance of the industrial city in the second quarter of the 19th century. Before that period, the city was a small highly compact zone in which people moved about on foot and goods were conveyed by horse and cart. But the early factories built in the 1840s were located along rivers and near rail stations at the edges of cities, and housing was needed for the thousands of people drawn by the prospect of employment. In time, the factories were surrounded byrapidly increasingmill towns of apartments and row houses that were close to the older, main cities. As a defense against this new drive and to enlarge their tax bases, the cities appropriated their industrial neighbors. In 1854, for example, the city of Philadelphiaintegrated most of Philadelphia County. Similar urban movements took place in Chicago and in New York. Indeed, most great cities of the United States achieved such status only by unifying the communities along their borders.In 1888, the first commercially successful electric traction line was developed. Within a few years thecarts drawn by horses were retired and electric streetcar networks crossed and connected every major urban area, fostering a wave of suburbanization that transformed the compact industrial city into a really great one.Glossary：suburbanization: 市郊化traction: 牵引力1.When did the process of suburbanization begin?A) During the appearance of city in the beginning of the 19th century.B) During the developed stage of the industrial city in the early 20th century.C) During the appearance of the industrial city in the second quarter of the 19th century.D) During the development of rural areas in the second quarter of the 19th century.2.How did most great cities of the United States achieve their status?A) By building more factories along the line.B) By unifying the communities along their borders.C) By absorbing more people from far and near.D) By enlarging their tax basis.3.In which year was the first commercially successful electric traction line developed?A) 1840.B) 1854.C) 1878.D) 1888.