TOEFL Reading: ETS-TOEFL阅读机经 - XU6MPPOAZ914M277L$

Which of the following can be inferred from paragraph 3 about changes in the demographics of cities during the nineteenth century? A. The reason most people left the city was to take jobs in the country. B. The middle class population increased. C. The population became more ethnically diverse. D. The working class population tended to live in the oldest housing.