The processes of urbanization, specialization, and trade in medieval europe led to
a decrease in economic opportunities for the lower class
the growth of the middle class in urban centers
a new system of bartering controlled by merchants
a decrease in opportunities for apprenticeship

The correct answer in this case is that it lead to a new system of bartering controlled by merchants. Merchants during medieval times in Europe played an amazingly important role because they basically could control the flow of trade and how goods could be distributed in certain cities for example. 

Iwill support us side.