为帮助大家在轻松愉快的氛围中掌握英语基础知识，本网站特提供以下资料，希望会带给你意想不到的收获：
Passage 4
Questions 12 to 15 are based on the following passage:
Before the mid-1860's, the impact of the railroads in the United States was limited, in the sense that the tracks ended at this Missouri River, approximately the center of the country. At the point the trains turned their freight, mail, and passengers over to steamboats, wagons, and stagecoaches. This meant that wagon freighting, stage-coaching, and steam-boating did not come to an end when the first train appeared; rather they became supplements or feeders. Each new "end-of-track" became a center for animal drawn or waterborne transportation. The major effect of the railroad was to shorten the distance that had to be covered by the older, slower, and more costly means. Wagon freighters continued operating throughout the 1870's and 1880's and into the 1890's. Although over constantly shrinking routes, and coaches and wagons continued to crisscross the West wherever the rails had not yet been laid. The beginning of a major change was foreshadowed in the later 1860's, when the Union Pacific Railroad at last began to build westward from the Central Plains city of Omaha to meet the Central Pacific Railroad advancing eastward from California through the formidable barrier of the Sierra Nevada. Although President Abraham Lincoln signed the original Pacific Railroad bill in 1862 and a revised, financially much more generous version in 1864, little construction was completed until 1865 on the Central Pacific and 1866 on the Union Pacific. The primary reason was skepticism that a Railroad built through so challenging and thinly settled a stretch of desert, mountain, and semiarid plain could pay a profit. In the words of an economist, this was a case of "premature enterprise", where not only the cost of construction but also the very high risk deterred private investment. In discussing the Pacific Railroad bill, the chair of the congressional committee bluntly stated that without government subsidy no one would undertake so unpromising a venture; yet it was a national necessity to link East and West together.
12. The author refers to the impact of railroads before the late 1860's as "limited" because ______.
A. the track did not take the direct route from one city to the next
B. passengers and freight had to transfer to other modes of transportation to reach western destinations
C. passengers preferred stagecoaches
D. railroad travel was quite expensive
13. What can be inferred about coaches and wagon freighters as the railroad expanded?
A. They developed competing routes.
B. Their drivers refused to work for the railroads.
C. They began to specialize in private investment.
D. There were insufficient numbers of trained people to operate them.
14. Why does the author mention the Sierra Nevada in line 17?
A. To argue that a more direct route to the West could have been taken.
B. To identify a historically significant mountain range in the West.
C. To point out the location of a serious train accident.
D. To give an example of an obstacle faced by the central pacific.
15. The word "subsidy" in line 27 is closest in meaning to ______.
A. persuasion
B. financing
C. explanation
D. penalty