Read the following passage on transport, and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 43 to 50.

“The economic history of the United States”, one scholar has written, “is the history of the rise and development of the capitalistic system”. The colonists of the eighteenth century pushed forward what those of the seventeenth century have begun: the expansion and elaboration of an economy born in the great age of capitalist expansion.

Our excellent natural resources paved the way for the development of abundant capital to increase our growth. Capital includes the tools – such as: machines, vehicles, and buildings – that makes the outputs of labor and resources more valuable. But it also includes the funds necessary to buy those tools. If a society had to consume everything it produced just to stay alive, nothing could be put aside to increase future productions. But if a farmer can grow more corn than his family needs to eat, he can use the surplus as seed to increase the next crop, or to feed workers who build tractors. This process of capital accumulation was aided in the American economy by our cultural heritage. Saving played an important role in the European tradition. It contributed to American’s motivation to put something aside today for the tools to buy tomorrow.

The great bulk of the accumulated wealth of America, as distinguished from what was consumed, was derived either directly or indirectly from trade. Though some manufacturing existed, its role in the accumulation of capital was negligible. A merchant class of opulent proportions was already visible in the seaboard cities, its wealth as the obvious consequence of shrewd and resourceful management of the carrying trade. Even the rich planters of tidewater Virginia and the rice coast of South Carolina finally depended for their genteel way of life upon the ships and merchants who sold their tobacco and rice in the markets of Europe. As colonial production rose and trade expanded, a business community emerged in the colonies, linking the provinces by lines of trade and identity of interest.

With what subject is this passage mainly concerned?