[单项选择]Mass transportation revised the social and economic fabric of the American city in three fundamental ways. It speeded up physical expansion, it sorted out people and land uses, and it 62 the inherent instability of urban life. By opening vast areas of unoccupied land for residential expansion, the buses, 63 , commuter trains, and electric trolleys pulled settled regions outward two to four times more 64 from city centers than they were in the pre-modern era. In 1850, for example, the borders of Boston lay 65 two miles from the old business district; by the turn of the century the 66 ex tended ten miles. Now those who could afford it could live far removed from the old city center and still 67 there for work, shopping, and 68 The new accessibility of land around the periphery (外围) of almost every, major city 69 an explosion of real estate development and fueled what we now 70 as ur
A. but
B. and
C. or
D. not