As towns grew, which group was most likely to take responsibility for making improvements to the town?

Merchant guilds

Explanation:

During the middle ages, when the town began to grow, Merchants were responsible for making improvements in it. The Guilds organized in medieval towns to maintain the standard of the crafts made by the artisans. The members of a merchants guild highly respected in society because of their hard work and crafts. In most European towns, merchant gentry exercised authority through its control of the urban structure.