The correct answer is B; Fields became more productive, spurring population growth.
Further Explanation:
When the fields became more productive the farmers had more food and could make more money. This had others coming to start their own farm and grow foods. Other ways medieval towns and cities had growth was the trade fairs that would be put up. This helped the cities and towns grow larger and have more of an economy.
When the towns and cities grew, they needed merchant guilds to form and take responsibility for the improvements in the towns and cities. They also were so much trading going on that they started using the credit system instead of using cash.
