参考答案：
(1)mass urbanization
(2) unprecedented trend
(3)major source
(4)farming
(5)manufacturing
(6)financing
(7)comfort and convenience
(8)transportation networks
(9)urbanization
(10)opposite
(11)smaller communities
(12)income level
(13)communities
(14)cultural background
(15)contact with
(16)challenge
(17)economic security
(18)ghettos
(19)destitute conditions
(20)inequality
