Urbanization and City Infrastructure

• (A) Urbanization is an ever-increasing trend; one that can be observed in areas throughout the world as economies begin to rely more on manufacturing and business for revenue. ■
• (B) Working and living in large cities is gradually replacing the traditional rural careers such as small-scale agriculture. ■
• (C) It is estimated that within the next century, more than half of the world’s citizens will reside in cities. ■
• (D)
  While some cities are planned, most cities are organic, meaning that urbanization in these areas takes place with little or no advanced planning. While the increase in urban areas and its population has yielded positive effects such as an increased concentration of businesses and more career opportunities, researchers have also discovered a host of detrimental effects on the areas in transformation from rural areas to urban centers.
  The concerns about urbanized areas worldwide differ somewhat in their relative importance, but many cite traffic congestion, inadequate public transportation, insufficient waste disposal facilities, inadequate solid waste collection, and a lack of water and sewage treatment facilities as primary concerns. One hundred years ago in Australia, the commute from Paramatta to the center of Sydney took approximately an hour by horse and cart. Today, the same trip in a car takes longer. Opponents of unplanned urbanization have also pointed out the destruction of agricultural land and animal habitat as a negative consequence of urbanization.
  Many of these problems could be eliminated, or at least mitigated, through the construction and maintenance of appropriate city infrastructure. Although the term is somewhat ambiguous, it was traditionally understood to mean roads and sewers. However, the U.S. National Research Council opted to widen the definition of public works infrastructure to refer to roads, bridges, mass transit systems, and water and waste management systems.
  Chief among the concerns of city dwellers is the issue of traffic jams and general congestion, and the corresponding difficulty in navigating the streets of any large urban area. Appropriate infrastructure, however, could serve as a useful tool in curtailing this problem. Two factors that exacerbate traffic congestion in a typical city are narrow streets and a lack of off-road parking, which would force many workers to park on the side of the road. Several solutions to the excessive traffic in urban areas have been proposed. Firstly, the construction of bypasses would eliminate the amount of traffic in the downtown areas, as travelers could use faster, more direct routes to arrive at their destination. Parking concerns could be addressed by constructing parking garages consisting of several stories. In this way, many cars could be stored in a relatively small amount of space.
  Closely related to the previous problem is the issue of inadequate public transportation. People will choose to ride buses; however, the system must be efficient and reliable. The establishment of a variety of mass transit systems such as subways, buses, and ferries could provide a feasible alternative to those that use their own vehicles to travel to their jobs in the city.
  Many cities have concerns about the problems involving waste collection and disposal. Along with education about waste diversion techniques such as composting and recycling, the development of city infrastructure can play a key role in ensuring adequate waste treatment. This would include the construction of easily accessible recycling facilities and appropriately placed composting facilities. In addition, urban areas should ensure there is a citywide transit system in place to collect solid waste.
  Finally, citizens in many urban areas have concerns regarding sewage treatment plants and water treatment facilities. The development of such facilities in an acceptable area, typically in a location outside of the city, could effectively deal with these concerns. Not only would this infrastructure improve the health of the citizens, but it would also benefit the environment by reducing the amount of pollution in the form of sewage entering water sources.

Look at the four squares [■] in the passage that indicate where the following sentence can be added to the passage.
Until the Industrial Revolution, this was the main occupation for the majority of people throughout the world.
Where would this sentence best fit

A．■ (Ａ)

B．■ (Ｂ)

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D．■ (Ｄ)

焊接时，使气体介质电离的种类有哪些？