What type of surfaces do trim tabs adjust in flight?

Trim tabs are small adjustable surfaces located on primary flight controls such as ailerons, elevators, and rudders. They are designed to assist pilots in maintaining aircraft stability and control during flight without the need for continuous input on the control surfaces. When a trim tab is deflected, it alters the aerodynamic characteristics of the associated primary flight control surface, allowing the aircraft to "trim" for a certain flight condition. This makes it easier to maintain level flight or a specific flight attitude without constant control stick pressure, thereby reducing pilot workload.

The other options, while related to the aircraft, do not serve the same function as trim tabs. Landing gear relates to the aircraft's landing system and does not involve in-flight adjustments for trimming. Propellers are primarily concerned with propulsion and thrust management, not stability in terms of control surfaces. Navigation instruments, while critical for situational awareness, do not have a role in adjusting flight control surfaces during flight. Hence, the role of trim tabs is specifically tied to the adjustment of primary flight controls.