The chief purpose of medieval fairs was to o
A. increase agricultural output
0
B. promote trade
0 C. help manors become self-sufficient
O D. protect the interests of craftworkers

B. promote trade

Explanation:

Medieval fairs were large scale fair that use to to held on every year in big towns and people come there from different cultures or regions for trade. People in this fair find various range of goods at a very cheap price because of the competition in the fair.  

The chief purpose of medieval fairs was to promote trade only as it allows people from different regions to come and sell their goods and increase the trade.

Hence, the correct answer is "B. promote trade".