I am a slow walker,but I never walk backwards.
我走得很慢，但是我从来不会后退。
A rapid means of long-distance transportation became a necessity for the United States as settlement (新拓居地)spread over farther westward. The early trains were impractical curiosities,and for a long time the railroad companies met with troublesome mechanical problems. The most serious ones were the construction of rails able to bear the load*and the development of a safe,effective stopping system. Once these were solved?the railroad was established as the best means of land transportation. By I860 there were thousands of miles of railroads crossing the eastern mountain ranges and reaching westward to the Mississippi. There were also regional southern and western lines.
The major problems with Americans railroad system in the mid 19th century lay in.
A. poor quality rails and unreliable stopping systems
B. lack of financial support for development
C. limited railroad lines
D. lack of a transcontinental railroad
讲解答案：
本题问的是19世纪中叶美国铁路系统存在的问题。作者在第一段第三句中指出，当时最严重的技术问题是the construction of rails able to bear the road和the development of a safe,effective stopping system，所以答案为A。这个问题与该句的比较考点(最高级)相联系The most serious ones。
