According to the news, what caused the growth of t

单项选择题

Questions 6 to 8 are based on the following news. At the end of the news item, you will be given 10 seconds to answer each question. Now listen to the news.

According to the news, what caused the growth of the US economy about 200 years ago

A．The new technology used to build roads.
B．The ability to transport goods over land.
C．The trade in grain and cotton.
D．The linking of smaller local roads into one long road.