Hello!
The Columbian Exchange was a exchange of animals, culture, food and technology, between the old and new world. Letter d).
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Primary sources are a example of first hand reports or eyewitness account
The answer to your question is: The emperors had lacked the leadership skills to rule the dynasty and the officials were also corrupt. Because of the corruption and mismanagement of the dynasty, a certain group led by Zhu Yuangzhang went against the dynasty and caused the fall.
