A limited number of systems required under FAR 23 pertain to which of the following for the PA-28-235?

The question refers to the limited systems required under FAR Part 23, which outlines airworthiness standards for normal, utility, acrobatic, and commuter category airplanes. Specifically, the PA-28-235 is a light aircraft that must comply with various regulations concerning safety and operational functionality.

When considering the fuel flow requirements, these are essential for ensuring the aircraft's propulsion systems receive the correct amount of fuel under various operating conditions. This is particularly important for certain flight profiles and operations that might require specific fuel management systems, limitations, and performance assessments.

In contrast, while cockpit controls, landing gear, and electrical systems are also critical to a plane's operation and safety, the requirements for these systems are generally broader and more comprehensive. They encompass numerous components and functionalities that don't fall under the "limited" classification specifically mentioned in the question. Therefore, fuel flow requirements represent a more focused aspect of systems that are outlined under FAR 23 for the PA-28-235.