A、 Why American industries grew rapidly in the nineteenth century.
B、 How advances in transportation helped American cities develop.
C、 Transportation between the cities of the United States.
D、 Great American inventors of the nineteenth century.

【正确答案】 B

【答案解析】解析：主旨题。根据The focus of today’s class is on an important element in the development of United Statescities，something the modern cities need to survive：efficient transportations可知本文谈论的是城市交通，结合全文，应该是城市交通的发展对城市发展的促进作用。因此，正确答案是B。

A、 It was no longer possible to keep horses.
B、 It was difficult to find jobs.
C、 They could no longer walk to work.
D、 They had to pay more for their housing.

【正确答案】 C

【答案解析】解析：细节题。根据Growth obviously meant greater distances between people’s home and their work places．People could no longer rely on walking．可知城市的扩大意味着家和公司之间的距离加大，人们再也不能走路上班了。因此，正确答案是C。

A、 They could be controlled independently.
B、 They were fire resistant.
C、 They could keep operating for a longer period of time.
D、 They offered more room for passengers.

【正确答案】 A

【答案解析】解析：细节题。根据They designers of electric trolley came up with the new control system that allowed eachpart to be powered independently and have its own breaks，what’s safer and more efficient than cable cars．可知除了速度更快，电车还能够独立运行，更加安全更加有效率。因此，正确答案是A。

A、 It made the subways much quieter.
B、 It brought electric light to the tunnels.
C、 It allowed passengers to breathe cleaner air in the tunnels.
D、 It allowed subways to be repaired inexpensively.

【正确答案】 C

【答案解析】解析：细节题。根据It solved one problem that the early English subways suffered from，unbearable smokeof steam engines that made breathing in the subway tunnels almost impossible．可知电车的出现使得地铁更换了动力，不再以蒸汽机为动力，解决了人们在地铁上难以呼吸的问题。因此，正确答案是C。