In the 18th century, New York was smaller than Philadelphia and Boston. Today it is the largest city in America. How to explain the change in its size and importance？
To answer this question we must consider certain facts about geography, history and economies. Together these three will explain the huge growth of America's most famous city.
The map of the Northeast shows that four of the most heavily-populated areas in this region are around seaports. At these points materials from across the sea enter America, and the products of the land are sent there for export across the sea.
Economists know that places where transportation lines meet are good places for making raw materials into completed goods. That is why seaports often have cities nearby. But cities like New York needed more than their geographical location in order to become great industrial centers. Their development did not happen simply by chance.
About 1815,when many Americans from the east coast had already moved to the west, trade mutes from the ports to the central regions of the country began to be a serious problem. The slow wagons of that time, drown by horses or oxen, were too expensive for moving heavy freight very far. Americans had long admired Europe's canals. In New York State a canal seemed the best solution to the transportation problem. From the eastern end of Lake Erie all the way across the state to the Hudson River there is a long trip of low land. Here the Erie Canal was constructed. After working for several years it was completed in 1825.
The canal produced an immediate effect. Freight costs were cut to about one-tenth of what they had been. New York City, which had been smaller than Philadelphia and Boston, quickly became the leading city of the coast. In later years, transportation routes on the Great Lakes were joined to routes on the Mississippi River. Then New York City became the end point of a great inland shipping system that extended from the Atlantic Ocean far up to the western branches of the Mississippi.
The new railroads made canal shipping not as important as before, but it tied New York even more closely to the central regions of the country. It was easier for people in the central states to ship their goods to New York for export overseas.
Exports from New York were greater than imports. Consequently, shipping companies were eager to fill their ships with passengers on the return trip from Europe. Passengers could come from Europe very cheaply as a result.
Thus New York became the greatest port for receiving people from European countries. Many of them remained in the city. Others stayed in New York for a few weeks, months or years, and then moved to other parts of the United States. For these great numbers of new Americans, New York had to provide homes, goods and services. Their labor helped the city become great.
Which of the following can be the best title for the passage？

A. The Development of Transportation in New York.
B. Exports and Imports of New York.
C. How New York Became America's Largest City？
D. How New York Exchanged with Europe？