Questions 14 to 17 are based on the following passage. At the end of the passage, you will be given 20 seconds to answer the questions. Now listen to the passage. According to the professor, what was the major change in the agriculture during the 19th century
A．Crop production became increasingly specialized. B．Economic depressions lowered the prices of farm products. C．New banking laws made it easy to buy farmland. D．The United States increased its agricultural imports.