[填空题]
What is suburbanization If by "suburb" is meant an urban{{U}}
(47) {{/U}}that grows more rapidly than its already developed
interior, the process of suburbanization began during the{{U}} (48)
{{/U}}of the industrial city in the second quarter of the 19th century.
Before that period the city was a small highly{{U}} (49) {{/U}}cluster
in which people move about on foot and goods were{{U}} (50) {{/U}}by
horse and cart. But the early factories built in the 1830s and 1840s were{{U}}
(51) {{/U}}along waterways and near railheads 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{{U}} (52)
{{/U}}by proliferating mill towns of apartments and row houses that abutted
the older, main cities. As a defense{{U}} (53) {{/U}}this encroachment
and to enlarge their tax base, the cities appropriated their industrial
neighbors. In 1854, for example, the city
