Final answer:
The action that fits the economic control functions described would involve the establishment of a central banking system as part of the government's regulatory role in the economy.
Step-by-step explanation:
The action that completes the diagram, which involves government economic controls on market activities and aims to deregulate the banking and financial sector while reducing protectionist policies, is most likely related to the establishment of a central banking system, as regulatory actions towards a national bank would fit within the parameters of these economic controls and functions. The government's role as a regulator includes overseeing businesses, ensuring fair competition, and establishing national banks, which are essential for a stable marketplace and a competitive free-market system. Additionally, the government reduces protectionist policies by managing tariffs and the overall economic policies that can affect business operations.