A power-driven boat underway in conditions of reduced visibility is required to sound what type of signal?

In conditions of reduced visibility, a power-driven boat is required to sound a prolonged blast at intervals of not more than two minutes. This signal is intended to provide a warning to other vessels in the area that the boat is underway, as visibility may be limited, making it difficult for other operators to detect its presence.

The use of a prolonged blast helps to ensure that the vessel's location is communicated effectively to others, thereby enhancing safety on the water during times when visibility is compromised. The practice aligns with the navigation rules and conventions established to help all mariners understand their surroundings and take appropriate actions.

Other options provided do not align with the regulations concerning reduced visibility; they describe signals that serve different purposes or contexts than what is prescribed for power-driven vessels under such circumstances.