22. Urban growth, also known as urbanization (城市化)，sped up dramatically with the coming of industrialization some 200 years ago. At that time, large numbers of people moved to cities in search of jobs, mostly in factories. But the most rapid growth has taken place over the past 50 years. While less than one-third of the world’s population lived in cities in 1950, about two thirds of humanity is expected to live in urban areas by 2030.
Urban is defined as “that which is characteristic of a city.” But what exactly is a city? In the past, walls may have defined a city. But today’s city boundaries are often unclear. Are suburbs parts of cities? Depending on the boundaries used, Tokyo can have a population of anywhere between 8 and 40 million people.
Cities make a lot of sense for humans. People are concentrated in a small space rather than being spread out over a large territory. This allows the government and others to provide more service such as water, electricity, and transportation to a larger number of people. Schools and shops are more easily accessible than in rural areas.
Cities have always been at the center of economic growth and technological advances. The promise of jobs and prosperity pulls people to cities. But their rapid growth has also brought with it many negative things: violence, poverty, overcrowding, health problems, and pollution. Many cities in developing countries in particular are growing too rapidly for their own good, with many residents unable to find jobs and forced to live in slums.(10分)

22.1  About years ago, people left for cities to find           .(2分)
A. food
B. clothes
C. jobs 
D. factories