单项选择题

Questions 14 to 17 are based on the following passage. At the end of the passage, you wilt be given 20 seconds to answer the questions.
What was the major change in agriculture during the 19th century

A．Specialized crops.
B．Farm machinery.
C．Extensive network of railroads.
D．Unbalance of supply and deman

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单项选择题

单项选择题

Questions 14 to 17 are based on the following passage. At the end of the passage, you wilt be given 20 seconds to answer the questions. What was the major change in agriculture during the 19th century 您的浏览器不支持 audio 元素。