The correct answer is B) increased trade with others
The reason that best explains why towns and cities grew during the Middle Ages was "increased trade with others."
In Medieval times, people used to sell their goods as peddlers but by 1300, merchants formally sold their goods in markets. Cargo ships arrive at the main ports in Europe and transported raw materials, natural resources, and minerals. By the 14th century, merchants in the city of Florence started to register operations in books; one for credits, the other for debts. Trade activity was an important part of the growth of cities in the Middle Ages.
The other options of the question were A) the spread of Black Death. C) invasion of Muslims. D) people came from all over to see Marco Polo.