What should be the pilot's action if an approach is not stable?

Answer: B — Initiate a missed approach.

If an approach is identified as not stable, the appropriate action for the pilot is to initiate a missed approach. A stable approach is one where the aircraft is correctly configured with an appropriate speed, descent rate, and glide path, all conducive to a safe landing. If these criteria are not met, it could lead to a dangerous situation during landing. Initiating a missed approach allows the pilot to safely exit the current unstable approach procedure and attempt the landing again or divert to an alternate airport if necessary. This decision prioritizes the safety of the flight crew and passengers over the urgency to land, ensuring that the risks associated with an unstable approach are effectively mitigated. In contrast, continuing the approach as planned could lead to a landing disaster or a runway overrun. Requesting to circle and re-approach, while a possible option in some scenarios, may not address the immediate instability if the underlying issues are not resolved. Lowering the landing gear at a higher altitude does not create a solution for an unstable approach and may further complicate the situation without the appropriate preparations being in place. Hence, initiating a missed approach is the safest and most prudent choice in the case of an unstable approach.