听力原文： Today I'm going to discuss transportation and communication in the early 19th century in the United States. At that time, inland waterways provided North America's most popular form. of long distance transportation. Travel by river was often more convenient than taking a wagon over primitive country roads, especially when shipping heavy loads of farm products or household goods. Where the natural water- ways were inadequate, shallow canals were built. The Erie Canal, opened in 1825, connected the Great Lakes with the upper Hudson River. It allowed settlers in the Great Lakes region to send their crops eastward to New York City at the mouth of the Hudson at a much lower cost. From there, crops could be shipped to other Atlantic ports. The construction of the Erie Canal also encouraged westward migration along inland waterways and helped populate the frontier. The City of Detroit grew up between two of the Great Lakes. Later a canal joined the Great Lakes with the Mississippi river system and Chicago became a thriving city. Politically the waterway system united the nation in a way few had imagined possible. By the mid-1800's faster and cheaper railroads became more popular and the canal system declined. Railroads could be used year round whereas canals were often frozen in the winter. During the first third of the century, however, transportation on rivers, lakes and canals aided greatly in the growth of the United States. Next week we'll discuss the railroads in greater detail. (33)