What action should a pilot take if within 3 minutes of a clearance limit and further clearance has not been received?

Answer: C — Start a speed reduction to holding speed in preparation for holding.

The appropriate action for a pilot who is within three minutes of their clearance limit and has not received further clearance is to start a speed reduction to holding speed in preparation for holding. This preparation is crucial for ensuring that the pilot can safely enter a holding pattern if required. By reducing speed to holding speed, the pilot is positioned to enter a standard holding pattern efficiently, which increases safety and adherence to air traffic control procedures. This proactive approach allows the pilot to respond effectively to potential changes in traffic management and ensures they are ready to hold without unnecessary delays or complications. The other options, while they seem to suggest maintaining situational awareness or readiness, do not adequately prepare the pilot for an immediate entry into a holding pattern, which is often required when further clearance is not received in a timely manner.