On sailboats and rowboats less than 7 meters in length, if regular running lights are unavailable, they may display ___________ or torch.

On sailboats and rowboats that are less than 7 meters in length, the regulations allow for the use of a lantern or torch in place of regular running lights when those lights are unavailable. This accommodation is made to ensure that small vessels can maintain visibility and be seen by other boats, thus promoting safety on the water. A lantern, which typically emits a steady light, is particularly suitable for this purpose as it can be easily deployed and provides sufficient illumination to indicate the presence and position of the vessel.

Using a lantern also aligns with maritime safety practices, as it provides a reliable light source in conditions where power-based running lights may fail. The other options—flare, beacon, and signal light—serve different purposes or require specific conditions for use, which may not be practical for small, unpowered vessels. Therefore, the option of using a lantern stands out as the most appropriate choice for maintaining visibility in a straightforward and effective manner.