Final answer:
Aileron trim with autopilot engaged is used to maintain the desired roll attitude. Hence the correct answer is option 3
Step-by-step explanation:
The use of aileron trim with autopilot engaged is to maintain the desired roll attitude. Aileron trim adjusts the aileron settings, which are the control surfaces on the wings that control the aircraft's roll or bank. The autopilot system uses the aileron trim to make small corrections to maintain the correct roll attitude during flight.
Hence the correct answer is option 3