Construction of the first rail network in the United States began in 1828. The first section was opened in 1830 and stretched 13 miles (21 kilometers). By 1835 there were over 1,000 miles (1,600 kilometers) of railroad in operation
along the Atlantic seaboard. Construction then moved toward the Midwest, eventually connecting the cities along
the Mississippi River with eastern ports. When gold was discovered in California, railroad construction increased
by six times its previous production rate. By means of rails, the country was soon connected from coast to coast,
which had a major impact on business and travel within the United States.

the railroad was .

A: experimental
B: undesirable
C: luxurious
D: advantageous