填空题

If by "suburb" is meant an urban margin that grows more rapidly
than it already developed interior, the process of suburbanization began 41______
during the emergence of the industrial city in second quarter of 42______
the nineteenth century. Before that period the city was a small highly
compact cluster which people moved about on foot and goods were 43______
conveyed by horse and cart. But the early factories built in the 1840’s
were locating along waterways and near railheads at the edges of cities, 44______
and housing was needed for the thousands of people drawn by the prospect
of employment. In time, the factories were surrounded by proliferating
mill towns of apartments and row houses that abutted the older, main cities.
As a defense against this encroachment and to reduce their tax bases, 45______
the cities appropriated their industrial neighbor. In 1854, for example, 46______
the city of Philadelphia annexed most of Philadelphia County. Similar
municipal maneuvers took place in Chicago and in New York.
Indeed, most great cities of the United States achieve such status 47______
only by incorporating the communities along their borders.
With the accelerate of industrial growth came acute urban 48______
crowding and accompanying social stress -- conditions that began to approach
disastrous proportions when, in 1888, the first commercially successful electric
traction line was developed. Within a few years the horse-drawn trolleys
retired and electric streetcar networks crisscrossed and connected 49______
every major urban area, fostering a wave of suburbanization that transformed
the compact industrial city into a dispersed metropolis. This first phase
of mass-scale suburbanization was reinforced by the simultaneous emergence
of the urban Middle Class, whose desires for homeownership in neighborhoods
far from the aging outer city were satisfied by the developers of single-family 50______
housing tracts.