What sound signal should be used by every other vessel that is not power-driven?

The correct choice identifies the specific sound signal that non-power-driven vessels should use to communicate their presence and intentions to other vessels when navigating, especially in conditions with restricted visibility. According to the COLREGs, sailing vessels should make one long blast followed by two short blasts when under sail, and this signal is recognized internationally as a means of indicating the type of vessel and its actions.

This practice enhances safety and situational awareness by clearly indicating to other vessels that the one making the signal is responding to the navigation rules that govern sound signals. Non-power-driven vessels, like sailing boats, are often slower or might maneuver differently than powered vessels, and this signal helps in conveying their status to nearby mariners.

In contrast, other listed responses are not aligned with established sound signal protocols for non-power-driven vessels, as they may apply to different vessels or scenarios that do not cover the necessary communication required for vessels under sail. This specificity helps ensure that all vessels can operate safely and effectively in shared waters.