Final answer:
Farm bills in the United States are typically renewed every five years by Congress, covering a wide array of agricultural and food policies.
Step-by-step explanation:
Farm bills that set agriculture and food policies are enacted every five years by the United States Congress. The correct choice from the given options would be 'b) four' if we strictly consider the choices provided. However, the actual cycle for the renewal of farm bills is typically every five years. These comprehensive bills cover a wide range of agricultural and food programs, including crop insurance, farm credit, conservation programs, rural development, and nutrition programs, among others.